A deity or other such powerful being asks you to become its agent on earth, if you choose to accept The deity gives the character an unusual pet as a gift. (work with your DM to determine details)
In adulthood you have an encounter with an unusual person, who as far as you can tell, has no home or family. You offer to help in anyway you can. After accepting your hospitality the stranger vanishes leaving a note "Your kindness will be remembered".
Political. A politcial enemy might inlcude a local magistrate, a noble who rules the region, or a monarch ruling the kingdom. the NPC might have offended a local ruler,become an outlaw, or a be a political rival.