"They’re playing Harper instead; he’s in my year and he’s an idiot."
-- Ginny Weasley (HBP14)
Harper was hit with a Bludger sent his way by Gryffindor Beater Coote. As he tries to knock Harry Potter off his broom, he calls Gryffindor Keeper Ron Weasley “your blood-traitor pal” – out of Referee Hooch’s hearing. He is, however, beaten in a race to the Snitch when Harry distracts him by shouting his guess that Draco had paid Harper to play – Slytherin lose the match (HBP14).
Harper is an occupational name for someone who plays a harp (Internet Surname Database).
As he started at the same time as Ginny Weasley, he is around a year younger than Harry.
Lexicon list of Seekers