7. Marvin ('A Hitchiker's Guide to the Galaxy')
Basic Function: To bitterly complain about his crippling loneliness and the lack of appreciation for his superior brain power while being forced to perform menial tasks.
Good or Bad: Marvin is extremely helpful throughout the course of A Hitchiker's Guide to the Galaxy, even as he manages to make Eeyore from Winnie the Pooh seem upbeat and happy by comparison.
Boldest Action: Shooting the evil Vogons with his "point-of-view gun" so that they share his hopelessly depressed attitude, thus robbing them of their will to fight.