My favorite character from Babylon 5 is Vir Cotto, played by Stephen Furst. He serves as comedy relief -- an awkward, clownish character out of his depth in interstellar politics. But Vir is utterly incorruptible. Although other, more cunning people, such as Londo Mollari and G'Kar, succumb to temptation, Vir refuses to make any moral compromises, ever. From the beginning, he correctly identifies the mysterious Morden as an agent of great evil and repeatedly warns Londo that his alliances of necessity will doom him and the Centauri Republic. And during the occupation of Narn, Vir risks his life to create phony documents that help 2,000 Narns escape the Centauri genocide.
Here is Vir in In the Shadow of Z'ha'dum, not just resisting temptation, but stomping it flat: