From there the skulls ranged upward in size to the three great monsters of song and story, the dragons that Aegon Targaryen and his sisters had unleashed on the Seven Kingdoms of old. The singers had given them the names of gods: Balerion, Meraxes, Vhaghar. Tyrion had stood between their gaping jaws, wordless and awed. You could have ridden a horse down Vhaghar’s gullet, although you would not have ridden it out again. Meraxes was even bigger. And the greatest of them, Balerion, the Black Dread, could have swallowed an aurochs whole, or even one of the hairy mammoths said to roam the cold wastes beyond the Port of Ibben.

- Book 1: A Game of Thrones

The hosts met on the broad plains of the Reach, amidst golden fields of wheat ripe for harvest. When the Two Kings charged, the Targaryen army shivered and shattered and began to run. For a few moments, the chroniclers wrote, the conquest was at an end . . . but only for those few moments, before Aegon Targaryen and his sisters joined the battle. It was the only time that Vhaghar, Meraxes, and Balerion were all unleashed at once. The singers called it the Field of Fire. Near four thousand men had burned that day, among them King Mern of the Reach. King Loren had escaped, and lived long enough to surrender, pledge his fealty to the Targaryens, and beget a son, for which Tyrion was duly grateful. 

- Book 1: A Game of Thrones

“Aegon’s dragons were named for the gods of Old Valyria,” she told her bloodriders one morning after a long night’s journey. “Visenya’s dragon was Vhagar, Rhaenys had Meraxes, and Aegon rode Balerion, the Black Dread. It was said that Vhagar’s breath was so hot that it could melt a knight’s armor and cook the man inside, that Meraxes swallowed horses whole, and Balerion . . . his fire was as black as his scales, his wings so vast that whole towns were swallowed up in their shadow when he passed overhead.” 

- Book 2: A Clash of Kings

Dragon names, and more; in old Valyria before the Doom, Balerion, Meraxes, and Vhagar had been gods. 

- Book 3: A Storm of Swords

Of the five dragons who had flown with Aenar the Exile from Valyria, only one survived to Aegon’s day: the great beast called Balerion, the Black Dread. The dragons Vhagar and Meraxes were younger, hatched on Dragonstone itself.

- Fire and Blood "Aegon's Conquest"

At Stokeworth a few crossbowmen loosed bolts at Visenya, until Vhagar’s flames set the roofs of the castle keep ablaze. Then they too submitted.

- Fire and Blood "Aegon's Conquest"

The Targaryen fleet, under Daemon Velaryon, left Blackwater Bay and turned north, for Gulltown and the Vale. With them went Queen Visenya and Vhagar.

- Fire and Blood "Aegon's Conquest"

When Torrhen Stark reached the banks of the Trident, he found a host half again the size of his own awaiting him south of the river. Riverlords, westermen, stormlanders, men of the Reach…all had come. And above their camp Balerion, Meraxes, and Vhagar prowled the sky in ever-widening circles.

- Fire and Blood "Aegon's Conquest"

Sharra Arryn had strengthened the defenses of Gulltown, moved a strong host to the Bloody Gate, and tripled the size of the garrisons in Stone, Snow, and Sky, the waycastles that guarded the approach to the Eyrie. All these defenses proved useless against Visenya Targaryen, who rode Vhagar’s leathery wings above them all and landed in the Eyrie’s inner courtyard. When the regent of the Vale rushed out to confront her, with a dozen guards at her back, she found Visenya with Ronnel Arryn seated on her knee, staring at the dragon, wonder-struck. “Mother, can I go flying with the lady?” the boy king asked. No threats were spoken, no angry words exchanged. The two queens smiled at one another and exchanged courtesies instead. Then Lady Sharra sent for the three crowns (her own regent’s coronet, her son’s small crown, and the Falcon Crown of Mountain and Vale that the Arryn kings had worn for a thousand years), and surrendered them to Queen Visenya, along with the swords of her garrison. And it was said afterward that the little king flew thrice about the summit of the Giant’s Lance, and landed to find himself a little lord. Thus did Visenya Targaryen bring the Vale of Arryn into her brother’s realm.

- Fire and Blood "Aegon's Conquest"

The sight of his sails, and the sudden appearance of Queen Visenya and Vhagar in the skies above Sisterton, took the heart out of the Sistermen; they promptly deposed Queen Marla in favor of her younger brother.

- Fire and Blood "Aegon's Conquest"

This was not something the Targaryens would allow to go unanswered. Later that same year, Visenya Targaryen appeared in the skies of Dorne, and Vhagar’s fires were loosed upon Lemonwood, Ghost Hill, and the Tor.

In 9 AC, Visenya returned again, this time with Aegon himself flying beside her, and Sandstone, Vaith, and the Hellholt burned.

...

Visenya and Vhagar brought fire and blood to Starfall.

- Fire and Blood "Reign of the Dragon: The Wars of King Aegon I"

The next two years were the years of the Dragon’s Wroth. Every castle in Dorne, save Sunspear, was burned thrice over, as Balerion and Vhagar returned time and time again.

- Fire and Blood "Reign of the Dragon: The Wars of King Aegon I"

Since the days of Old Valyria, it had ever been the custom of House Targaryen to burn their dead, rather than consigning their remains to the ground. Vhagar supplied the flames to light the fire.

- Fire and Blood "The Sons of the Dragon"

At the high table, Queen Visenya rose and stalked from the hall without the king’s leave. That night she mounted Vhagar and returned to Dragonstone, and it is written that when her dragon passed before the moon, that orb turned as red as blood.

- Fire and Blood "The Sons of the Dragon"

The Dowager Queen mounted Vhagar and brought fire and blood to the riverlands as once she had to Dorne. In a single night, the seats of House Blanetree, House Terrick, House Deddings, House Lychester, and House Wayn were set aflame.

...

And the dragons came. Vhagar first, as the sun was rising, then Balerion, just before midday. But they found the gates of the city open, the battlements unmanned, and the banners of House Targaryen, House Tyrell, and House Hightower flying side by side atop the city walls.

...

The city gates were opened, and Targaryen banners raised along the walls. Even before Vhagar’s wings were sighted, Lord Hightower’s men were rousting the Most Devout from their beds and marching them to the Starry Sept at spearpoint to choose a new High Septon.

- Fire and Blood "The Sons of the Dragon"

In their place, he decreed, a great stone “stable for dragons” would be erected, a lair worthy of Balerion, Vhagar, and their get. Thus commenced the building of the Dragonpit.

- Fire and Blood "The Sons of the Dragon"

Princess Aerea had known Vermithor and Silverwing during her time at court, but she had never been allowed too close to them. Here she could visit with the dragons as often as she liked; the hatchlings, the young drakes, her mother’s Dreamfyre…and greatest of them all, Balerion and Vhagar, huge and ancient and sleepy, but still terrifying when they woke and stirred and spread their wings.

- Fire and Blood "Birth, Death, and Betrayal Under King Jaehaerys I"

“Only one answer makes sense. Recall, if you will, that Balerion was the largest and oldest of the three dragons that King Aegon and his sisters rode to conquest. Vhagar and Meraxes had hatched on Dragonstone..."

- Fire and Blood "Jaehaerys and Alysanne: Their Triumphs and Tragedies"

Prince Baelon lingered only long enough to partake of the feast that evening before galloping back to King’s Landing to complete his quest and become a dragonrider. Never one to be overshadowed, he had long since chosen the dragon he wished to mount, and now he claimed her. Unridden since the death of the Dowager Queen Visenya twenty-nine years before, the great she-dragon Vhagar spread her wings, roared, and launched herself once more into the skies, carrying the Spring Prince across Blackwater Bay to Dragonstone to surprise his brother Aemon and Caraxes.

- Fire and Blood "The Long Reign - Jaehaerys and Alysanne: Policy, Progeny, and Pain"

Meleys was as swift a dragon as Westeros had ever seen, easily outpacing Caraxes and Vhagar when she and her brothers flew together.

- Fire and Blood "The Long Reign - Jaehaerys and Alysanne: Policy, Progeny, and Pain"

Jaehaerys Targaryen and his sons Aemon and Baelon had been waiting as well, and as Morion’s fleet beat its way across the Sea of Dorne, the dragons Vermithor, Caraxes, and Vhagar fell on them from out of the clouds. Shouts rang out, and the Dornish filled the air with scorpion bolts, but firing at a dragon is one thing, and killing it quite another. A few bolts glanced off the scales of the dragons, and one punched through Vhagar’s wing, but none of them found any vulnerable spots as the dragons swooped and banked and loosed great blasts of fire. One by one the ships went up in gouts of flame. They were still burning when the sun went down, “like a hundred candles floating on the sea.” Burned bodies would wash up on the shores of Cape Wrath for half a year, but not a single living Dornishman set foot upon the stormlands.

- Fire and Blood "The Long Reign - Jaehaerys and Alysanne: Policy, Progeny, and Pain"

Far easier to speak of Prince Baelon’s wroth, and how he came down upon Tarth on Vhagar, howling for vengeance. The Myrish ships burned as Prince Morion’s ships had burned nine years earlier, and when the Evenstar and Lord Boremund descended on them from the mountains, they had nowhere to fly. They were cut down by the thousands and left to rot along the beaches, so every wave that washed ashore for days was tinged with pink.

Baelon the Brave played his part in the slaughter, with Dark Sister in his hand. When he returned to King’s Landing with his brother’s corpse, the smallfolk lined the streets screaming his name and hailing him as a hero. But it is said that when he saw his mother again, he fell into her arms and wept. “I slew a thousand of them,” he said, “but it will not bring him back.” And the queen stroked his hair and said, “I know, I know.”

- Fire and Blood "The Long Reign - Jaehaerys and Alysanne: Policy, Progeny, and Pain"

A fiery young maiden, freshly flowered, Lady Laena had inherited the beauty of a true Targaryen from her mother, Rhaenys, and a bold, adventurous spirit from her father, the Sea Snake. As Lord Corlys loved to sail, Laena loved to fly, and had claimed for her own no less a mount than mighty Vhagar, the oldest and largest of the Targaryen dragons since the passing of the Black Dread in 94 AC.

- Fire and Blood "Heirs of the Dragon: A Question of Succession"

In those cities, far removed from the woes of Westeros and the power of the Triarchy, their welcome was less rapturous. Everywhere they went, however, huge crowds turned out for a glimpse of Vhagar and Caraxes.

The dragonriders were once again in Pentos when Lady Laena learned she was with child. Eschewing further flight, Prince Daemon and his wife settled in a manse outside the city walls as a guest of a Pentoshi magister, until such time as the babe was born.

- Fire and Blood "Heirs of the Dragon: A Question of Succession"

After three days of delirium, Lady Laena passed from this mortal coil. She was but twenty-seven. During her final hour, it is said, Lady Laena rose from her bed, pushed away the septas praying over her, and made her way from her room, intent on reaching Vhagar that she might fly one last time before she died. Her strength failed her on the tower steps, however, and it was there she collapsed and died. Her husband, Prince Daemon, carried her back to her bed.

- Fire and Blood "Heirs of the Dragon: A Question of Succession"

Even at ten, Aemond Targaryen did not lack for boldness. The king’s gibe stung, and he resolved not to wait for Dragonstone. What did he want with some puny hatchling, or some stupid egg? Right there at High Tide was a dragon worthy of him: Vhagar, the oldest, largest, most terrible dragon in the world.

Even for a son of House Targaryen, there are always dangers in approaching a dragon, particularly an old, bad-tempered dragon who has recently lost her rider. His father and mother would never allow him to go near Vhagar, Aemond knew, much less try to ride her. So he made certain they did not know, sliding from his bed at dawn whilst they still slept and stealing down to the outer yard where Vhagar and the other dragons were fed and stabled. The prince had hoped to mount Vhagar in secrecy, but as he crept up to the dragon a boy’s voice rang out. “You stay away from her!”

The voice belonged to the youngest of his half-nephews, Joffrey Velaryon, a boy of three. Always an early riser, Joff had sneaked down from his bed to see his own young dragon, Tyraxes. Afraid that the boy would raise the alarm, Prince Aemond shouted at him to be quiet, then shoved him backward into a pile of dragon droppings. As Joff began to bawl, Aemond raced to Vhagar and clambered up onto her back. Later he would say that he was so afraid of being caught that he forgot to be frightened of being burned to death and eaten.

Call it boldness, call it madness, call it fortune or the will of the gods or the caprice of dragons. Who can know the mind of such a beast? We do know this: Vhagar roared, lurched to her feet, shook violently…then snapped her chains and flew. And the boy prince Aemond Targaryen became a dragonrider, circling twice around the towers of High Tide before coming down again.

But when he landed, Rhaenyra’s sons were waiting for him.

Joffrey had run to get his brothers when Aemond took to the sky, and both Jace and Luke had come to his call. The Velaryon princelings were younger than Aemond—Jace was six, Luke five, Joff only three—but there were three of them, and they had armed themselves with wooden swords from the training yard. Now they fell on him with a fury. Aemond fought back, breaking Luke’s nose with a punch, then wrenching the sword from Joff’s hands and cracking it across the back of Jace’s head, driving him to his knees. As the younger boys scrambled back away from him, bloody and bruised, the prince began to mock them, laughing and calling them “the Strongs.” Jace at least was old enough to grasp the insult. He flew at Aemond once again, but the older boy began pummeling him savagely…until Luke, coming to the rescue of his brother, drew his dagger and slashed Aemond across the face, taking out his right eye. By the time the stableboys finally arrived to pull apart the combatants, the prince was writhing on the ground, howling in pain, and Vhagar was roaring as well.

- Fire and Blood "Heirs of the Dragon: A Question of Succession"

Thus it was not a raven who took flight for Storm’s End that day, but Vhagar, oldest and largest of the dragons of Westeros. On her back rode Prince Aemond Targaryen, with a sapphire in the place of his missing eye.

- Fire and Blood "The Dying of the Dragons: The Blacks and the Greens"

“We have more,” said Princess Rhaenys, the Queen Who Never Was, who had been a dragonrider longer than all of them. “And ours are larger and stronger, but for Vhagar. Dragons thrive best here on Dragonstone.” She enumerated for the council. King Aegon had his Sunfyre. A splendid beast, though young. Aemond One-Eye rode Vhagar, and the peril posed by Queen Visenya’s mount could not be gainsaid.

- Fire and Blood "The Dying of the Dragons: The Blacks and the Greens"

“At what cost?” Princess Rhaenyra wondered. “My sons would be riding three of those dragons, I remind you. And it would not be nine against four. I will not be strong enough to fly for some time yet. And who is to ride Silverwing, Vermithor, and Seasmoke? You, my lord? I hardly think so. It will be five against four, and one of their four will be Vhagar. That is no advantage.”

- Fire and Blood "The Dying of the Dragons: The Blacks and the Greens"

Munkun writes that the prince and Lord Borros were haggling over dates and dowries on the morning Lucerys Velaryon appeared. Vhagar sensed his coming first. Guardsmen walking the battlements of the castle’s mighty curtain walls clutched their spears in sudden terror when she woke with a roar that shook the very foundations of Durran’s Defiance. Even Arrax quailed before that sound, we are told, and Luke plied his whip freely as he forced him down.

Mushroom would have us believe that the lightning was flashing to the east and a heavy rain falling as Lucerys leapt off his dragon, his mother’s message clutched in his hand. He must surely have known what Vhagar’s presence meant, so it would have come as no surprise when Aemond Targaryen confronted him in the Round Hall, before the eyes of Lord Borros, his four daughters, septon, and maester, and twoscore knights, guards, and servants.

- Fire and Blood "The Dying of the Dragons: A Son for A Son"

Outside the storm was raging. Thunder rolled across the castle, the rain fell in blinding sheets, and from time to time great bolts of blue-white lightning lit the world as bright as day. It was bad weather for flying, even for a dragon, and Arrax was struggling to stay aloft when Prince Aemond mounted Vhagar and went after him. Had the sky been calm, Prince Lucerys might have been able to outfly his pursuer, for Arrax was younger and swifter…but the day was “as black as Prince Aemond’s heart,” says Mushroom, and so it came to pass that the dragons met above Shipbreaker Bay. Watchers on the castle walls saw distant blasts of flame, and heard a shriek cut the thunder. Then the two beasts were locked together, lightning crackling around them. Vhagar was five times the size of her foe, the hardened survivor of a hundred battles. If there was a fight, it could not have lasted long.

Arrax fell, broken, to be swallowed by the storm-lashed waters of the bay. His head and neck washed up beneath the cliffs below Storm’s End three days later, to make a feast for crabs and seagulls. Mushroom claims that Prince Lucerys’s corpse washed up as well, and tells us that Prince Aemond cut out his eyes and presented them to Lady Maris on a bed of seaweed, but this seems excessive. Some say Vhagar snatched Lucerys off his dragon’s back and swallowed him whole. It has even been claimed that the prince survived his fall, swam to safety, but lost all memory of who he was, spending the rest of his days as a simpleminded fisherman.

- Fire and Blood "The Dying of the Dragons: A Son for A Son"

Then came an answering roar. Two more winged shapes appeared: the king astride Sunfyre the Golden, and his brother Aemond upon Vhagar. Criston Cole had sprung his trap, and Rhaenys had come snatching at the bait. Now the teeth closed round her.

Princess Rhaenys made no attempt to flee. With a glad cry and a crack of her whip, she turned Meleys toward the foe. Against Vhagar alone she might have had some chance, but against Vhagar and Sunfyre together, doom was certain. The dragons met violently a thousand feet above the field of battle, as balls of fire burst and blossomed, so bright that men swore later that the sky was full of suns. The crimson jaws of Meleys closed round Sunfyre’s golden neck for a moment, till Vhagar fell upon them from above. All three beasts went spinning toward the ground. They struck the ground so hard that stones fell from the battlements of Rook’s Rest half a league away.

Those closest to the dragons did not live to tell the tale. Those farther off could not see for the flame and smoke. It was hours before the fires guttered out. But from those ashes, only Vhagar rose unharmed. Meleys was dead, broken by the fall and ripped to pieces upon the ground. And Sunfyre, that splendid golden beast, had one wing half torn from his body, whilst his royal rider had suffered broken ribs, a broken hip, and burns that covered half his body. His left arm was the worst. The dragonflame had burned so hot that the king’s armor had melted into his flesh.

- Fire and Blood "The Dying of the Dragons: The Red Dragon and the Gold"

Supremely confident in his own prowess as a warrior and the might of his dragon, Vhagar, Aemond was eager to take the battle to the foe.

- Fire and Blood "The Dying of the Dragons: The Red Dragon and the Gold"

That left only Vhagar. No living dragon could match Vhagar for size or ferocity, but Jace reasoned that if Vermax, Syrax, and Caraxes were to descend on King’s Landing, even “that hoary old bitch” would be unable to withstand them.

- Fire and Blood "The Dying of the Dragons: The Red Dragon and the Gold"

Let him descend from the high ground and cross the Red Fork with fire and sword, whilst Ser Criston Cole marched forth from King’s Landing, accompanied by Prince Aemond himself on Vhagar. The two armies would converge on Harrenhal to crush the “traitors of the Trident” between them. And if his uncle emerged from behind the castle walls to oppose them, as he surely must, Vhagar would overcome Caraxes, and Prince Aemond would return to the city with Prince Daemon’s head.

- Fire and Blood "The Dying of the Dragons: The Red Dragon and the Gold"