HIS STORY
Ideas:
He was orphaned during the
Great War.
Royalty found him and he was trained at Castle Hyrule to guard one of the royalty. Unfortunately, during an attack on the castle, he was separated from the one he was meant to protect and they were killed. In shame, he has left the castle, trying to find some redemption for his dishonor.
He uses his abilities to help those in need, like a sellsword, most times just working for a meal and a place to clean up and rest.
The Poe Esper, Tien, might have bonded with him in the Hylian Royal grave yard where he was praying and asking for forgiveness of the one he failed. He might see it as a sign of hope.