Muezzin (pronounced "myoo-ez-in" or "moo-ez-in"), from Arabic مُؤَذِّن, mu'adhdhin, refers to the man who performs the call to prayer (adhan) five times a day.
The muezzin is not a religious leader, but an upstanding member of the mosque who is chosen for his voice, skills, and good character.
He often cares for the mosque building as well, making him somewhat comparable to a Christian verger.