Luke is the son of Lucius Fox, a man high up in Wayne industries and close friends to Bruce Wayne. Due to this Luke well of and had a comfortable life.
However even though he came from a rich family, Luke wanted to join the Marines. But on a mission Luke’s team were killed. This left Luke with PTSD and was discharged. On returning home Luke had a panic attack at a 4th of July party when the the fireworks went off.
Due to this Luke’s dad and Bruce decided that Luke should start training with Bruce. This lead Luke into the secret that Bruce was Batman, and later lead to Luke becoming Batwing.