Cormac McLaggen is a Gryffindor student in the year above Harry Potter.

From the Story

Harry Potter and the Half-Blood Prince

Discovered in chapter 15, The Unbreakable Vow

Cormac attends Professor Slughorn's party as Hermione's date. He is left under the mistletoe by Hermione, after regaling her non-stop with accounts of his greatest Quidditch saves as Keeper.