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)
A strange woman gives you an ornate box sealed with wax and hoarsely whispers "It's up to you now, keep it safe, keep it from ... them." It is not until the woman drops dead at the character's feet that the dagger in her back becomes obvious.
As an adult you joined a rebellion against the local ruler, if successful you are outlawed, if it failed you escape, with only friends and family knowing your involvement. (Work with your DM to detirmine the details)