You receive a mysterious message from persons unknown, the message details a dangerous secret which is now up to you to keep safe. (work with your DM to determine details)
An evil, despotic ruler orders all persons of your Race, birthplace, and approximate age put to death. As far as you know, you are the only one to escape this heinous act. (work with your DM to determine details)
In adult life you gain a rival who seeks to undo your character, they will attempt to hinder your efforts until they get what they want. (work with your DM to determine details)