Eddie Redmayne

Eddie Redmayne as Reginald Cattermole

Reginald Cattermole, nicknamed 'Reg' by Mary MacDonald , is a fairly softspoken Hufflepuff at Hogwarts school.  He is a canon character in the Harry Potter books, whom we meet in book seven "Harry Potter and the Deathly Hallows" when Ron, Hermione and Harry break into the ministry to steal Slytherin's Locket from Umbridge. He is the one Ron takes a Polyjuice potion to look like. 

It is believed that Mary MacDonald and Reginald will end up married, as his wife, whom we also meet in DH, also bears the name Mary.