Is Lord Voldemort the headmaster of Hogwarts?

Answer 1

Voldemort always wanted to teach Defence Against the Dark Arts but Dumbledore refused to give him a job. Voldemort then cursed the position so nobody could hold it for more than one year.

In the 1991/1992 school year he shared Professor Quirrel's body. Quirrel taught Defence Against the Dark Arts.

Answer 2

No. Lord Voldemort took over the Ministry and appointed one of his Death Eaters as Minister for Magic - who then appointed Severus Snape as the headmaster of Hogwarts. Voldemort thought he was in charge of the school, but Snape was working with Dumbledore's portrait to protect the students.

Answer 3

Severus Snape.

He was sort of right. Severus was a death eater before he realised Voldemort planned on killing the one person he always loved, Lily Potter. Snape then join the Order of the Phoenix and pretended to be a death eater, spying on the order when he was really an order member spy on the death eaters and passing selected information to the death eaters.

Answer 4

Professor Quirrell was sharing his body and had Lord Voldemort on the back of his head, but Quirrell was still very much in control and wasn't actually Voldemort.

Answer 5

Harry always suspected Professor Snape of working with Voldemort. In some ways, it turned out he was right.

Answer 6

In book 1, Harry Potter believes that Severus Snape is working for Voldemort.