My two favorite backstories are

Techlan Que, the halfling former snake oil salesman. His dad's in jail for selling snake oil, but he'll be out in a year or two. In the meantime Tek and his brother are working to put their kid sister through wizard school and send money home to ma because she doesn't have a paying job

And Simon Blackwood Jr., a kobold rogue. His parents were high ranking thieves' guild members before they retired to take care of their kids, but they took one last job to clear some kobolds out of a cave. They couldn't bring themselves to smash the only egg, so they brought it home and raised him as their own son. Now he's 8 years old, fully grown and out looking for work, much to his mother's dismay. She'd prefer he to to school with his older sisters, aged 11 and 13