Clark Sawyer is Reed Van Kamp's older stepbrother from his remarried father, Winston Davis.His mother is Lianna Sawyer-Davis. Clark's first (and so far only) legitimate canon prose appearance is in the drabble Brother Actwritten by CP Coulter, which, while it will not appear in the FF.net canon, will be referenced to and should be taken as such.
From descriptions and information given by the author, Clark is nineteen years old, six-foot-five, blond with blue eyes, and built strongly. He is a celebrity in his own right: he is foremostly a popstar, being a member of a boy group ("the thousand-screaming-fangirls-kind"), and has also recently forayed into the acting world and is doing very well at it. It also appears that he and Julian Larson both work together in the fictional TV series Something Damaged ("a mash of 90210 and One Tree Hill").
Reed expresses that he has yet to really interact with each other properly, as he'd only seen Clark once. But from their conversation in Brother Act, it would appear that Clark, as a person, is a good-natured, patient young man who goes above and beyond the call of duty in certain degrees. He appears to be very good to Reed in spite of never having met him, and looks after his well being, aware that their shared father has no time for him.
His working with Julian in the acting world has, irrevocably, linked him somewhat romantically to the actor in fandom.