Use their name - they're just like any othe teacher. Most head's don't like extra special attention.
I'm a Deputy headmaster
When addressing a headmaster of a private school, it's best to use their formal title followed by their last name, such as "Headmaster Smith" or "Mr. Smith." If the headmaster has a doctoral degree, you may also refer to them as "Dr. Smith." In written correspondence, starting with "Dear Headmaster" or "Dear Mr./Dr. Smith" is appropriate. Always maintain a respectful tone, reflecting the formal nature of the school environment.
headmitress
I am the headmaster.
The headmaster, Merle Ambrose, is located in the commons, in the "Headmaster's tower"
Headmaster Merle Ambrose is the headmaster and he has a talking owl for a pet and he knows alot of things.
Igor Karkaroff was the headmaster of Durmstrang
The Headmaster - book - was created in 1992.
headmaster
Edward Grant - headmaster - died in 1601.
Edward Grant - headmaster - was born in 1540.
Tony Little - headmaster - was born in 1954.
George Butler - headmaster - was born in 1774.