Bishop is a chaotic evil ranger that serves no allegiance for too long. Based at the 'Sunken flagon' tavern, where he was waiting, for who knows how long, for the owner Duncan to call upon a debt. When that time finally comes, Bishop joins forces with the PC's party and sets off to track the gythyanki who kidnapped Shandra Jerro after assaulting the tavern. Bishop is merciless, backstabbing, homicidal and mistrustful. All of these characteristics stem from his troubled childhood in Luskan, where he burned an entire village down in an act of defiance and impulse. Betrays the PC in the NWN2 campaign and joins Black Garius. In the final confrontation you can persuade him to betray Garius, or you can kill him. If you are of an evil disposition, you can join with him along side the King of Shadows and kill off all of the good-aligned party members. Although irreparably destructive, Bishop has a certain corsair mercenary likeness about him. He was initially planned as a romance option for female PCs but eventually this was deleted.
In Mask of the Betrayer, Bishop's lack of a deity serves as a plot point. You encounter Bishop in a dream, where you see him half-consumed by the wall of the faithless. He says that he takes nothing back and that he is not remorseful; he is in fact happy because he will finally know total erasure.
Source: Wikipedia, "List of Neverwinter Nights characters", available under the CC-BY-SA License.