My favourite main character (and almost whole character) of Fallout series is, without any doubt, the first, the only and the great Vault Dweller. So, i have to say he has done very difficult things (almost impossible). Destroying a whole mutant army? Surviving the Glow? Are you kidding me, man? The fucking Vault Dweller has done tons of awesome quests being, as his name says, only a normal vault dweller (maybe the Albert Cole's greatness?). The Vault Dweller is incredibly badass, i would say he is the greatest hero of the wasteland. Then, the Courier. Wow, man, if you are able to survive a shot in the head without any protection, you are, for sure, a hard son of a bitch. Then, the Chosen One. Being only a tribal, he destroyed a fucking army like the Enclave and he killed crazy aberration Frank Horrigan. Then, the Lone Wanderer (is so similar to the Vault Dweller) and then, the Sole Survivor.
By saying that, i can't really understand how the Vault Dweller, without any known data about the wasteland, only Vault 15's location, could survive and, then, do all that amazing things. Yes, it's true, he was raised in a Vault, but, man, he's a true hero, unkillable (if that word really exists).
Referring to the thread, i think Ulysses is a lower (nearly as good) version of the Courier. He's fucking amazing. I wouldn't say crazy, but not sane. He survived tons of quests too.