Crabbe and Goyle
House: Slytherin, 4th Year
For the life of us, we can't find any differences between Crabbe and Goyle in Goblet of Fire. They basically seem interchangeable with one another. These two Slytherin fourth-years are Malfoy's muscle. They follow him everywhere and do exactly what he asks them to do, because they're both as dumb as a bag of hammers. Whenever Malfoy and the Gryffindors get caught in a fight, one or both of these boys wind up with some horrible curse. Crabbe, in particular, sprouts "little tentacles all over his face" (37.123) after their end-of-term fight on the Hogwarts Express to London.
Both Crabbe and Goyle have fathers who are Death Eaters. Voldemort addresses them by name in the Little Hangleton graveyard. No wonder their sons like to cluster around Draco Malfoy: it's basically an imitation of their fathers' Death Eater social dynamic.