it's a bit like asking "who was jesus" though:
http://en.wikipedia.org/wiki/Trotskyshort version: lenin's power rival/comrade at arms. got a bolshevik icepick to the head for his troubles in mexico later on. he was, in theory, less authoritarian and into less centralized, more democratic leadership. got outmaneuvered by lenin more or less at every turn.
edit: and was used as the ultimate apostate in the stalinist version of this strange, strange religion.
double edit: "Trotsky's great-granddaughter, Nora Volkow (daughter of Esteban Volkov), is currently head of the U.S. National Institute on Drug Abuse." yeesh!
even shorter version: they're all communist scum. the world is better off that they're dead.