A syndrome affecting non-protagonist main characters in films, video games and books wherein said characters role is to teach and or aid the protagonist in their quest. BKS curses the afflicted to be doomed to sacrifice themselves for the sake of the protagonist.
Typical character traits include compassion, intelligence, wisdom and some specialised form of badassery.
Ben Kenobi suffers from a fatal case of Ben Kenobi syndrome in the Star Wars Episode IV. He spends the first half of the film rescuing luke sywalker from danger, teaching him the ways of the force. Unfortunately for Ben, he has become far to useful a character for luke to have around to save his arse. The BKS causes Ben to confront Darth Vader on the death (and die)to give Luke, han, chewie and the newly rescued leia time to escape the space station on the millenium falcon.