Charles Mayhew is the current headmaster of Hogwarts.
When Headmaster Barnabus Ehrlich died rather suddenly from a heart attack, the board found itself in a bit of a tight spot. This was only shortly after the Highgate Rampage incident (one 16 year old wizard, 15 dead, 20 injured) and the debate about control on education was still hot. Voices in the ministry were suggesting more direct control on magical schools. No one had a wish to repeat the debacle of Dolores Umbridge, so a backhand deal was made on retired chief auror Charles Mayhew. He accepted to come back from retirement, partly because Hugo Allbrass , an old friend and colleague of sorts, was already a teacher there and would be able to help him.