Who is Alcibiades from Symposium and what is their importance?

Alcibiades arrives at the Symposium, drunk, shortly after Socrates finishes his speech. He accuses Socrates of deceit and resents that Socrates will not be his lover. Alcibiades offers Socrates both his riches and his good looks. Some of Alcibiades accusations become a part of the criminal indictment against Socrates at a later date.