One question:
*why* will he only play a first level character?
Because he thinks it looses story and plotline? Because he likes to be weak?
There a few things you may be able to do:
*Powerful races. If he doesn't want a high-level character, he can have a high HD monster as a race. Just hook up with some advice on ECL's on these boards, and you should be good to go: low levels, and he's not that much weaker than the rest (by ECL +14, those guys BETTER be getting some monster hit dice, or I have bigger doubts about the ECL idea than I thought....)
*Let him write the tale of his adventuerer *until* he met the PC's. If he's not a 1st level character, he's been through some adventures before, and bringing in an already-seasoned adventurer could help him get over that "realism" hump. Certainly, the PC's aren't the most powerful people in the world? Develop this guy like an NPC, and then have him join the party. Is he a well-known swordsman? Is he a slayer of dragons from a kingdom over? A mysterious traveler from beyond the sea? An elderly elf who has seen twenty wars already? If he's as big a drama queen as you're making him sound, this should be his dream: he gets to legally make up any convoluted novella he wants about his character. As the DM, you can use this for plot hooks or just say that you might. Either way, he's not playing a budding adventuerer. He's playing someone who's a hero already, whose interests mesh with the party's.
*Give him a template. Might add a bit of resilience to him, so that it won't be so easily to accidentally kill him (or at least no easier than it would be to any other character). Make him a were-something, or an undead or a half-golem or whatever your imagination can concoct. It could be incapacitating ("Sorry, you're a zombie, new PC time! But you can't walk out, because I didn't kill your old one..."), or just something to give him a slight edge he may not have right now.
*Let him play his 1st level nobody...but make him a prince or something, perhaps a budding celestial or the reincarnation of some important figure. He can go on adventures, and he's likely to survive...and then just level him up like nobody's business (the XP that a 15th level party gets should bump him up helluh-fast).
Seriously, it's a bit tough to stop him from doing something you don't like if I don't know the motive behind it...
Either way, don't be forced to play with him. There are probably methods that will stop it from going that far, but sometimes two people's idea of how to have fun with an RPG just don't mesh. I mean, I may be friends with a Vampire LARPer, but, dude, I ain't gonna have fun doing that, you depressed whackjob.
Yeah, try having him play potent races or meshing with the story.
Or, if you're really getting annoyed, here's a plan: afflict his character with a template. Say, make him a Werebear or a Vampire or something. Something that'll up his power without discarding his original character. If you're really a RAT BASTARD DM, I'd either make his character undead ("hey, you said don't kill your character, and I didn't....permenantly..."), or give him some sort of incapaciting injury that doesn't kill him. ("you're not dead, but with Wisdom as a nonability, you're technically an object. I'm affraid you'll have to create a character that will work")
I guess the main issue is that he shouldn't simultaneously be insiting on playing a weak character and then forbidding you from killing said weaking. That's the risk of playing a low-level character, dood. Suck it up, and stop yer whining, candy-bottom.
