Lord Voldemort
Voldemort sat on the large chair on the dais that had been provided for him, watching the girls and their partners as they took to the floor. He did not dance. Umbridge had told him that several of her students would be honoured to speak to him.
He had created the Slytherin Academy with the aim of recruiting as many wizards and witches as possible to his Ministry, and to train the best of the best into his inner circle. So he didn't mind attending such things, especially as it reminded any upstarts who was really in charge.