Jeffrey was the holographic son in the Doctor's family program, who turned rebellious after B'Elanna Torres added realism.
Jeffrey was one of the two children in the Doctor's holodeck family. In its original version he was an ideal son, eager to please his father and enthusiastic about learning.
In Real Life, Torres's changes turned Jeffrey into a moody teenager who fell in with a group of young Klingons and pushed back against the Doctor's authority. The Doctor was baffled by how to reach him, but the tragedy that struck his sister Belle brought father and son closer together.