From Halopedia, the Halo wiki
Before 850 BCE
Ossis 'Xellus was a Sangheili warrior and the firstborn son of Ussa 'Xellus, Kaidon of Xellus.
Ossis 'Xellus was hatched in the city-state of Xellus, born to Kaidon Ussa and Sooln 'Xellus. He was slain in battle, likely during the War of Beginnings.