I once needed a new character for Fantasy Hero. Couldn't come up with anything original, so decided to steal from fiction. So I started with Conan, but then thought - what if he got religion when he got older? I eventually came up with a slave->gladiator->soldier->high priest character, and then based his physical appearance off of Wilt Chamberlin in Conan the Destroyer. He's been played in one campaign, and is a featured NPC in another. He's in his late 40s, a high priest / fighting order grandmaster, and has been exiled to the campaign area (Harn) after losing a political battle. He hates it there, but knows that doing a good job is the only way to get back in power, and so does his best. Although possibly the best fighter in the area, it means nothing, as he rarely ever uses a weapon or has on armor. He's now a high priest, heavily involved in politics, backroom deals, and plotting against the opposing churches (and heretics in his own).
First long-term superhero campaign I ever was in, I needed a character for a new game. Came up with a Captain Atom (DC Comics - the silver guy) knockoff. Your basic flight, power blast, strength, etc. But, I tend to be ruthless in battle (no Silver Age niceguy crap from me), and though unintentional, he started taking on overtones of the Punisher very quickly. Through time, and several "radiation accident" makeovers, he became a disgruntled bounty hunter that was well known for killing bad guys. Of course, there were numerous arguments and fights with his team members, who did not appreciate his methods. More than once he stomped off to go solo for a time. For the one semester I took a break from school, the player of the pacifist mentalist took him a second character, and kept him just as deadly and unsociable. Everyone loved the character, but he was not a team player, and was finally retired in favor of new characters that were. When I later created my own setting, he was ported in as the archtypical bloodthirsty bounty hunter, and has remained a key NPC. His name - Orion.
Whenever I play on MUDs (rare nowadays), my main character is always Barzic, and is a fighter type. He's always a grumpy old guy, bitching about how the young kids don't respect the traditions, and how things were so much better back in the day before you had your pansy gate spells and overpowered magic items. Walked uphill through the snow both ways to school type, or so he tells the stories. Exploration is my primary enjoyment, so I quickly become the person that knows the entire MUD, from walking to any spot, to the location of every creature, and the stats on every single piece of equipment in the game. Having all this knowledge helps in maintaining the persona of the Old Guy, even when I am actually one of the newer players.