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.
Minerva McGonagall served as the interim head until the board of governors (under control of Voldemort) appointed Severus Snape as Headmaster. After Snape abandoned his post, McGonagall took control again. She was officially appointed the headmistress after the final battle and retired a few years later.
It is unknown. Minerva McGonagall retired and was not headmaster during the epilogue.
Lord Voldemort killed her with the killing curse and fed her body to Nagini.
Lord Voldemort was never looking for Maryland in the series.
No, but they are related. Harry's father, James's great-grandfather was Ignotus Peverell who's niece was Merope Gaunt. Merope Gaunt is Tom Riddle's/Voldemort's mother. So Voldemort is a distant cousin of Harry's dad.
1) Lord Voldemort wanted him to, 2) Dumbledore wanted him to.
Severus Snape was appointed headmaster after Lord Voldemort (indirectly) took over the Ministry of Magic.
Armado Dippet was the headmaster when Tom Riddle (aka Lord Voldemort) attended Hogwarts.
Lord Voldemort died in the Great Hall at Hogwarts. In the movie, this was changed to the Courtyard at Hogwarts.
Lord Voldemort was never the headmaster, Severus Snape was the headmaster when Voldemort was in power. After Snape ditched his position before the battle, McGongall automatically became the headmistress. After the war, she held this position formally for a few years before retiring. It is unknown who was the head after her.
In the great hall at Hogwarts.
In the Great Hall at Hogwarts.
Severus Snape. In the end (after Voldemort's defeat): Professor McGonagall.
He was in Slytherin. In fact, he was the last remaining relative of Salavar Slytherin.
On the back of Quirrel's head.
None of the professors were Lord Voldemort. Quirinus Quirrell, the Defence Against the Dark Arts Professor, was sharing his soul with Voldemort and had his face on the back of his head.
Harry Potter was never headmaster of Hogwarts. After defeating Voldemort he became an Auror and then later, Head of the Auror office. It is unknown when he died, although he was still alive in 2017 when he was 37.