Logan Harper was a Hogwarts graduate and Slytherin and the brother of Luke Harper. After Hogwarts, he joined the Death Eaters and attempted to recruit Luke. He was injured in a duel with Aurors in 1976 and went to Luke for help. Luke asked his then girlfriend, Lily Evans, to heal him. Lily did and tried to persude Luke to turn him over to the Ministry, but Luke refused and Logan disappeared.
He was killed by auror Jack Lathe while evading arrest.