Unggoy Major
From Halopedia, the Halo wiki
Only one step higher than Minor Grunts in rank, these red-armored Grunts are slightly more powerful than their lesser counterparts. They often lead Grunt Minors in battle. However, even with increased rank, Grunts of any kind hold no power over any other forces in Covenant society.
Combat
Major Grunts usually wield Plasma Pistols and Needlers, but occasionally one will carry a Fuel Rod Gun in later stages of the games. They are far more aggravating than Minors. Especially on higher difficulties, they throw grenades very frequently, although not without first yelling out a helpful "Clear!" or "Everybody duck!". In Halo 2, though, they're quiet sometimes, or yells "Holy light!"
Major Grunts are easy to kill no matter what you use, but it is more efficent to either melee attack them from behind or kill them with a headshot using a Pistol or a Battle rifle