A Kohen is a male of Shevet Levi (the tribe of Levi) whose lineage can be traced back to Aharon HaKohen (Aharon the Priest). The kohanim (priests) were designated as those who perform the avodah (service) in the Beit HaMikdash (Temple). All kohanim who are above the age of twenty-one and do not have a feature that makes the unable to work, are obligated in the avodah of the Mikdash. A kohen, with the exception of the Kohen Gadol (high priest) is known as a kohen hedyot (regular priest). Other than their role as those who do the service in the Mikdash, they are charged with teaching the nation Torah along with the rest of Shevet Levi.