Head counselors are demigods in charge of their cabin as well as all their half-siblings (if they have any as some cabins have only one person) at Camp Half-Blood. They choose their activities, go to war counsels, lead them to meals, and do cabin inspection. The role of head counselor is automatically given to the eldest demigod, but if a younger camper has completed more quests, they can challenge the head counselor and have a duel with them, and whoever wins becomes head counselor. An example being in The Lost Hero when Piper McLean challenged Drew Tanaka after completing her quest. Another way is that the current head counselor willingly steps down. For example, Jake Mason willingly gave up his position to Leo Valdez during The Lost Hero. They are the Greek equivalent of Roman Centurions at Camp Jupiter.
Known Head Counselors
Hera's cabin is honorary. Because she is the goddess of marriage she "doesn't run around having affairs".
Even though Artemis is a virgin goddess, her cabin is occupied by her Hunters when they stay at the camp.