Although I caution my players from investing too much effort into the back story of a 1st level character who could easily get incinerated by the radioactive eye-beams of a mutant cyborg random encounter, I do enjoy it when a back story emerges. Which coincidentally enough, usually happens sometime after the character achieves 2nd level.
One of the players in my Planet Algol campaign has a character, Nigel Nightbreaker, a British Fighting-man who, due to my ability score requirements for weapons house rules, uses a halberd in melee. He is also upset that he can't find ale or beer anywhere.
However, while talking after a session, we decided that on account of him being a polearm wielding Englishman that he was most likely a Beefeater who had been guarding British archaeological treasures in the Tower of London. One eve while investigating a strange glow emanating from a bizarre artifact he was transported to Planet Algol 210? A.D.