Minerva McGonagall becomes Headmistress.
The head master before Dumbledore was Armando Dippet.
The school's Head Master
On the back of Quirrel's head.
Snape
Snape becomes head master and controls the school with two other death eaters Alecto and Amycus while Voldemort tracks down Harry Potter.
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.
yes he is the head master but it should be the deputy
No. Voldemort gained his first followers at Hogwarts. Although it is unknown what year Professor Quirrell was born in, he certainly wasn't old enough to be have been at school with Voldemort. Quirrell met and joined Voldemort in 1990 during a year long sabbatical.
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.
After Voldemort was killed, Kingsley Shacklebolt (the new Minister of Magic) asked Harry to become an Auror(which is what Harry wanted to do since his fourth year at Hogwarts). Harry reformed the Auror Department and became its Head in 2007.
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.
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.