Cormac McLaggen

Cormac McLaggen is a Gryffindor student one year above Harry. He is introduced for the first time during the train journey to Hogwarts in Half-Blood Prince as a member of Horace Slughorn's Slug Club, due to his uncle's close ties with the Ministry of Magic. Cormac is shown as an unsympathetic Gryffindor character. His Gryffindor bravery is both a strength and a flaw: he is foolhardy and proud, bordering on arrogant. He plays roles both in the fortunes of the Gryffindor Quidditch team and in Hermione's love life. Cormac tries out for the position of Keeper when Harry becomes captain, having missed the tryouts the previous year due to his eating a pound of Doxy eggs on a bet. However, Hermione jinxes him with the Confundus Charm, causing him to miss his last save and thus helping Ron retain his spot on the team. Cormac does not take his loss well, accusing Ginny of favouritism by giving Ron easy shots to block.
Cormac fills in during Gryffindor's match against Hufflepuff as Keeper when Ron is unable to play due to poisoning, but his debut is disastrous, as he orders the team about instead of focusing on his own position, knocks Harry unconscious with a Beater's bat, and contributes to Gryffindor's lopsided 320-60 loss, thus earning him universal dislike among his housemates, and Harry and the team in particular. Cormac also briefly becomes a pawn in the escalating tensions between Ron and Hermione, as he is Hermione's date at Slughorn's Christmas party in retaliation for Ron's relationship with Lavender Brown. The plan backfires when she becomes offended by McLaggen's boorish behaviour, and she leaves him stranded under the mistletoe and avoids him for the remainder of the party.
Rowling said she named the character McLaggen simply because she liked the surname.[14]
Cormac will be played by Freddie Stroma in the film version of Half-Blood Prince.