Severus Snape was a former Death Eater (follower of Lord Voldemort), who later became a double agent and a member of the Order of the Phoenix, headed by Albus Dumbledore and then the Potions master at Hogwarts. After Voldemort's return, Dumbledore ordered Snape to go back to Voldemort and act as a spy for him. Voldemort accepted Snape back, believing that Snape had been gathering valuable information for him at Hogwarts when he was away. In Harry Potter's sixth year at Hogwarts, Snape was assigned to the post of Defence Against the Dark Arts teacher, the job which he had been applying for since he first joined the Hogwarts staff. Nearing the conclusion of the same year, several Death Eaters invaded Hogwarts, and cornered Harry and Dumbledore. Draco Malfoy was under orders from Voldemort to kill Dumbledore, but he was unable to do so, so Snape killed Dumbledore instead, cementing his position as one of Voldemort's most trusted Death Eaters. The next year, Snape was appointed Headmaster at Hogwarts after the Death Eaters invaded the Ministry of Magic and took control of it. A battle at Hogwarts broke out, which, in the end for Snape, resulted in Voldemort killing Snape over the Elder Wand, a wand which was believed to be unbeatable. In his final moments, Harry Potter came across Snape, and Snape showed Harry memories of his past, revealing that he had been acting under Dumbledore's orders the whole time, and had been protecting Harry.