Two-Bit is the jokester of the gang and—at eighteen—is also one of the oldest (just behind Darry). He talks non-stop and has a smart comment about everything no matter whom he's talking to, even if it's the police. Although he's a ladies' man and dabbles in petty thievery, Two-Bit seems like a warm-hearted guy... at least in terms of the people he cares about.
Two-Bit doesn't directly drive any of the action of the plot, even though he's involved in a lot of it. And although he gives Dallas a knife in the hospital, the knife doesn't play a role in the story's outcome, unlike the knife Johnny uses to kill Bob. Still, Two-Bit helps us get a sense of Pony's world and the variety of people in it.