Piano teacher, composer, former pianist, and all-around rageholic in the "Prisoner of Love!" story of romance comic Love Diary #13 (February 1951).
He tutors poor, downtrodden piano devotee Ruth Andrews, but is a real jerk about it. He loves real pianist Rubenstein, and takes Ruth to see him. But Derek stares so intently at him, it weirds her out.
It turns out that Derek's hands were injured in WWII somehow and he can't play the piano like he used to, and it drove him round the bend.
Ruth Andrews gets away from him and tries playing the piano for fun, but it just isn't the same without his cold, angry screeching, and she realizes she loves him. What. No, seriously, that's the script. It's just not right. When she confides her love to him, she sees his beautiful "Ode to Ruth" he's been composing. Then he confides his love for her and suddenly morphs into a normal human being.
The postscript says he's one of America's most promising composers, thanks to "Ode to Ruth," and that she plays his music.