"They’re playing Harper instead; he’s in my year and he’s an idiot."
-- Ginny Weasley (HBP14)
Harper is a the replacement Seeker on the Slytherin Quidditch team in 1996 during his fifth year, when Draco Malfoy was too unwell to play as Seeker in their match against Gryffindor (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
From the Web
Harry Potter Wiki: Harper