N'tho 'Sroam is a low-ranking Elite warrior who is part of the army of the Covenant Separatists in Halo 3. Not much is known about him except that after the Elite race allied itself with Humanity, N'tho personally gave detailed information to UNSC intelligence on how Brute society functioned, as well as technological details on their signature "Chopper" vehicles.
All this information, including his name, comes from sources outside Halo 3. The only role he plays at all in-game is that he is the character controlled by player three in 3- or 4-player co-op mode. Oddly, he never opens his right eye, the leading theory being that it was damaged in battle.