In the beginning, Aon Ní was alone.  One day, he had a sister, Aon Rud.  Aon Rud wanted to play and to create.  Aon Ní only wanted to be left alone.

Because Aon Ní would not play with her, Aon Rud created children to play with.  She named them Éagruth and Eagar.  For some time, they lived quite happily together.  Éagruth was creative and adventurous, always seeking new ideas and never cleaning up after himself.  Eagar was responsible and intelligent, and delighted in making rules for their games and building things in Éagruth's wake.  Aon Rud's wisdom helped temper the differences between her sons.

Aon Ní was appalled.  So much noise.  So much life.  It would be much better, he thought, to go back to being alone.

One day, Aon Ní approached Éagruth while he was playing alone.  "Your brother always bosses you around," he said.  "And your mother allows him.  Would it not be better if you were in charge?"  "But Uncle," Éagruth replied, "I love my mother and I love my brother.  And it is right that he should rule, being older."  Aon Ní feigned surprise.  "But did you not know, little one," he said, "that you are older?"

Éagruth blinked and stared.  He had not known.

"You are not even his brother," said Aon Ní, leaning in conspiratorially.  "You are his cousin.  My son.  And I made you before him.  It does not seem right that they now order you."

Éagruth was despondent.  He loved his mother deeply, but now believed that she had lied to him.  Every gentle rebuke, every loving guidance she had given him now sprang to mind as proof that she despised him, and favored Eagar.  He could not take the pain of it.  It twisted his already disordered mind, and slowly drove him mad.  Until he slew Aon Rud, and sat by her side, crying.

Aon Ní crept in, preparing to strike him down before finding and killing Eagar.  He would, at last, be alone again.  As Aon Ní reared up, suddenly Aon Rud's body moved.  Eagar sprang from her remains, holding her ribs before him like a giant claw.  He closed them around Aon Ní, and fastened them with her sinews.  He fashioned a cage around his uncle, trapping him forever.

Eagar would never forgive Éagruth, but he set to work making the world out of what remained of his mother.  Whenever Éagruth knocked something down or tore something up, he sighed and made something new out of the mess.

He worried, too.  He worried that Aon Ní would escape.  He knew neither he nor his brother would be safe.  He had children of his own--Ghrian and Gaelach.  He set them on patrol around the world, forever on the lookout for signs of their grand uncle.