Who is Begbie from the motion picture, Trainspotting?

Begbie is the classic violent, ill-tempered, bad addict. He has no sympathy for anyone and is perpetually looking out for himself alone. He attacks everyone who seems to get in his way, even if they are simply strangers in a bar. Begbie seems to be the mastermind behind the final drug deal and he is enraged to discover that Renton has stolen from the rest of the group.