About the character 
He was the violent boyfriend of Ryan's biological mother: Dawn Atwood. He supported the woman decision to kick her son out of the house after Ryan was arrested. He has problems with alcohol and cocaine. He also was abusive to Ryan and his mother. A.J. also has children of his own, but they never appeared on screen.
Dawn broke up with him, shortly after kicking Ryan out. She also makes the decision to leave and leave him.