He is Tse'huk, leader of the first Na'vi Clan. Very old clan, the Ni'awve.
Tse'huk was the Olo'eyktan of the Ni'awve clan, the first Na'vi clan.
Tse'huk being detained by the RDA.
He was captured by the RDA in the unobtanium mine near Hell's Gate. The soldiers planned on executing him, but Jake Sully and Neytiri were able to rescue him thanks to Grace Augustine's information. Tse'huk revealed that the humans were going to try and destroy the Tree of Souls, and so Jake flew off on his banshee to stop them.
Note that the events of the mobile phone game are considered non-canonical. Numerous spelling discrepancies exist in the mobile game; Tse'huk may be a misspelling of Tsu'hak, the leader of the Ni'awve attested in the iOS and Android version of the game.