Derek is the captain of the football(soccer) and rowing teams.
He is known as a bit of a womanizer, as he is said to have dated any cheerleader he can get his hands on.
Derek is friends with Julian Larson and Logan Wright III, he and Julian are probably originally friends through Logan,
Derek and Logan became friends because they once shared a room, Derek feels rightly that he is the only one at Dalton (most of the time) who will put up with Logan's idiosyncrasies and Logan feels the same about him.
Derek, as almost the mother of the Stuart trio, pushing Logan to take his pills, and being the first and only one to notice Julian's attraction to Logan.
As for his family, it is know that Derek has a little sister, Amanda, who he is very fond and protective of. Amanda still goes to Elementry school and looks up to her big brother, who she thinks is 'awesome'.