Well in response to a few of the more frequent things that were said; first of all I don't know if I would feel the same if the character type he played every time was more helpful, or a healer type. I think that I would have the same problem with it, and see it as a lack of creativity and trying new things, but I've never played with anybody who consistently plays the exact same helpful character every game, so I can't really say.
Second; I know it's not a crime to like one type of character and want to play them a lot, but I think doing so every single game without exception is pushing it a bit. I honestly feel like if he wants to play that type of character so badly it might be better to join a campaign that's expected to last a long time, that way he can keep playing the same one character for a long time, rather than recreating that character over and over for every little one-shot he joins.
And finally, he's kind of like this outside the game, it's just not so obvious. Within the game, every player but him is switching around their personalities with each new character and he isn't, so it's very noticeable. Outside the game on the other hand, nobody really switches around their personalities much, so the fact that he has his strong, lasting interests isn't really unusual or as annoying as it is at the table.
And I'm pretty sure ninjology doesn't get accepted in Scrabble... Not without a fight at any rate.