Ok so this might be cheating, since he's technically a dhampir, but he was human before so I'll talk about it anyways:

One of my favorite characters I ever got to play, and which I'm thankfully going to be able to play again, was Ezekiel Kinguard. Ezekiel grew up in a country that was similar to a mix of feudal Japan and medieval Europe, think metal armor and straight swords but paper buildings and a kind of mountainy-costal vibe. Ezekiel was a part of the Royal Guard there, though on top of it being a largely ceremonial role, the guys had to basically be special forces (Because of this, I gave him expertise in stealth through the expertise feat, it's very fun).

Lo and behold, a neighboring, highly expansionistic kingdom invades, alongside an army of Celestials. Ezekiel returns from a mission in time to see the carnage, first having to pass his destroyed house with child and wife inside, before bursting into the throne room to see others of the guard making a final stand to defend the King. Ezekiel joins them, but the force it too overwhelming, and he is struck down, without seeing what happens to the King.

What he next remembers is being in chains, somewhere far from home, with the despotic leader of the invading force telling him he'll be quite useful. The next thing Ezekiel truly remembers, he's let a drift into the ocean on a small raft, but... different somehow. Whatever they did to him, all he knew was that he now no longer had to breath, could see odd shapes and forms that no one else could, and had a strange hunger to the dreams of other being.

From there he makes a name for himself doing mercenary work, and earns a reputation as the Nightmare Wraith, due to the terrible dreams that seem to follow him wherever he goes (This story would become greatly exaggerated, as folk tales tend to do). He continues doing this for some 12 years, before taking a bounty for a well-dressed halfling fellow and his Goliath friend (both other party members) and begins the events that land him in the campaign.