Half Blood Prince
Albus Dumbledore hired Wilkie Twycross to come teach the sixth years at Hogwarts to apparate, who presumedly had been doing this every day for a while now. The description given to him is he's 'Oddly colourless, with transparent eyelashes, wispy hair, and an insubstantial air, as though a single gust of wind might blow him away'.  He was not very liked by the students and received names such as 'Dung-head' and 'Dog-breath', which he wasn't happy about. Harry Potter, although in the same year, wasn't of age at the time as you must be seventeen or close to it to learn apparition. This was also the case with Draco Malfoy and Seamus Finnigan.
 Portrayals within films
Wilkie's roll was omitted from the film adaption in Harry Potter and the Half-Blood Prince.