Buck Mulligan/Stephen Dedalus
In terms of energy and humor, Mulligan is a great character. Hearing him joke around in "Telemachus" or "Oxen of the Sun," one might think that he'd be a pretty fun guy to hang out with. So what is Stephen's problem? Both Stephen and Mulligan are extremely well educated (though Stephen is at another level), and both have cast off many of the traditional religious beliefs and societal norms that are supposed to guide their lives. Yet Mulligan is a mocker. Everything is comic fodder for him, and we see little sign that he believes in anything or cares about anyone. In this capacity, he is a threat to Stephen. Not only because Stephen can tell that Mulligan is jealous of him and takes this out by mocking him, but because Stephen doesn't want to fall into the sort of cheap nihilism that rules Mulligan's life. As stubborn as Stephen is, we can begin to see his virtues when we contrast him with his friend Buck Mulligan (as well as some of his most dangerous faults).