He was stationed initially on a tiny island in front of the second Shield Tower protecting the main Citadel of the Ark. Johnny and Arby fought past his pack on a Hornet and destroyed the Anti-Air Wraith guarding the island. The resulting explosion killed the majority of Hermitus's pack and what few remained later died of their injuries.
Hermitus was left stranded on the Ark after the Flood were destroyed by the newly reactivated Halo. Hermitus survived the Halo's fire by hiding behind a rock, and the primitive Forerunner technology could not get to him. He then emerged to find the Flood destroyed.
He managed to survive on the Ark by living off the corpses of Humans from the battle, and he stored their bodies in a massive refrigerator that used to be used for storing Flood. Hermitus lived to be a very old Brute before finally dying on the Ark at the age of 102. He was the last of his kind when he died, but he did not know this at the time. His body was found much, much later by Human explorers to the Ark, but they passed it off as just another casulty of the war and disposed of his corpse and armour in much the same was as they did for the other dead Brutes lying around.