Toby Belch is Olivia's free-loading uncle and the ring leader of a raucous little crew of party animals. He whoops it up 24/7, drinking, eating, belching, singing, dancing, and trash-talking his way through Twelfth Night. The only thing Toby doesn't do is sleep. Toby Belch, like his name, is pretty disgusting. But, his obnoxious ways are what make him such a significant figure in the play. His gluttony and rebellious attitude embody the spirit of Twelfth Night festivities, which were all about over-indulgence and the inversion of social order. For more on this, go to "What's Up with the Title?" and come right back.
Sure, Toby's lots of fun to hang out with at parties, but he's also kind of a jerk. He totally uses his drinking buddy, Sir Andrew Aguecheek, who supports Toby's extravagant lifestyle. He even plays a mean trick on Aguecheek when he convinces him to pick a fight with "Cesario" and then calls Aguecheek a wimp behind his back. He also doesn't give a flying rat if his late night carousing disturbs his niece while she grieves for her dead brother.
Toby thinks it's time for Olivia to snap out of it and get married. (In a way, he's right, but he's still a jerk.) In fact, Toby tries his best to broker a marriage between Olivia and Aguecheek so he can secure his extravagant lifestyle. His (failed) attempts at playing match-maker reveal his selfishness, sure, but Toby's attempts to marry Olivia to someone from the same social rank also gives voice to the play's concern with social ambition. For Toby, the thought of Olivia marrying a man outside of her "class" is pretty threatening. (Check out more on this by going to "Society and Class.") This is part of the reason why Toby goes berserk when he learns that Malvolio is a social climber with fantasies of marrying Olivia. Of course, Toby mostly hates Malvolio because he's a major party-pooper who disapproves of Toby's lifestyle.