"The leader of a monastery" is called an abbot, or abbess. Abbot for the male gender, abbess for the female gender. Hope that helps!
which kind of monastery? the leader in a Catholic monastery is an Abbot. you'd have to do some more research to find out what the highest rank monk in a Buddhist monastery is named.
An abbot is the leader of a Monastery. IF the leader was a woman, she was called the abbess.
The leader of a Monastary is known as an Abbott.
Abbot or abbess