The character is adopted into a Wealthy family. If he is an orphan, it is a true adoption. If he has living parents, he is treated just like a son. (work with your DM to determine details)
Martial training: In adolescence you trained with the weapons of your people and learnt how to use them proficiently (work with your DM to determine details)
While foraging or hunting for food, you have an encounter with a trapped predatory beast. Instead of slaying it, you free it. The freed beast disappears. Later, you are trapped by a falling log. The same beast reappears, aiding and freeing you.