Alpha Jiralhanae
From Halopedia, the Halo wiki
The Alpha Jiralhanae is a Covenant Jiralhanae (Brute) rank. Gargantum was an Alpha Jiralhanae. Brutes of this rank appear to be of equal rank to Elite Zealots, as they serve as ship masters.
It is unclear if "Alpha" is just another name for one of the existing Brute Ranks (Likely Brute Captain or Brute Chieftain) or if it is an entirely different rank in itself.
