In your opinion, who's the most useless character in the game? I'd add a pole, but there are so many characters in the game... here's a http://fallout.wikia.com/wiki/Fallout_3_characters though, showing the characters.

My pick is Stockholm. It's extremely difficult to get up to his catwalk and he only has one dialogue option, in which he wonders how you even got up to the catwalk. Lucas Simms might mention, but i don't think so.
The only other reference to him is that he has a tab of 8 caps in Moriarty's Saloon, and his theorized connection to the password of the jail cell in Vault 101.

Yup, Stockholm is definitely just there for flavour, if that.