The first horde was created by Gul'dan to serve his will. After the orcs escaped to Azeroth, they formed the horde that we know today.
The orc shaman thrall led the horde until the cataclysm, stepping down to become a shaman to commune with the elements. He then ultimately struck garrosh hellscream down on Draneor.
Sylvanas windrunner was killed by arthas during the war against the lich king, becoming an undead banshee after. When she rose to power of the title of warcheif of the horde after vol'jins death after the events of the broken shore, she went on a murderous campaign just to become immortal. After she killed varok saurfang in a mak'gora, she fled the horde.
After the events of the fourth war, the leaders of the horde decided not to have a warcheif, and instead be run by a council.
Playable races: orc, tauren, undead, goblin, blood elf, troll
Faction capital: Orggrimar