Unggoy Majors are higher in rank than Minors and are slightly more powerful than their lesser counterparts in terms of strength, intelligence, leadership, and morale. They sometimes lead small squads of Minor Grunts into battle. However, even these higher-ranked Unggoy hold no power over any other forces in Covenant society.
Grunts Majors mostly appear leading a squad of Grunt Minors under the leadership of any Sangheili, even a Minor. They usually appear wherever Grunt Minors do. They are found in almost all the levels in the Halo trilogy where you find the Covenant. In Halo 3, not much changes for Grunt Majors, as they are still lead by the lowest ranks of the highest Covenant society, which at this time are Brutes. They are usually led by Brute Minors to Brute Captain Ultras. They also fight alongside Drones, Jackals, and even Hunters on occasion.
They are seen in combat as decorated in lucid red-colored armor (similar to their Elite counterparts), contrary to the orange armor of Minor Grunts. They are more courageous as well, often staying to fight under conditions that would make their lesser brethren flee. If all of their commanders, Sangheili or Jiralhanae, are killed, they will sometimes continue to fight. However, they still aren't very courageous and can more often be observed fleeing along with rest, though they are more likely to go kamikaze than the Minors. They usually fight alongside a combined team of other Unggoy and Kig-Yar, and have command over the former. Grunt Majors are the first enemy to wield the hand-held Fuel Rod Gun in the Halo series. They were first seen utilizing these deadly weapons after the player had destroyed the first Pulse Generator in the Halo: Combat Evolved level, Two Betrayals. They also know to wear and use equipment on occasion. In Halo 2, particularly on the level Regret, they are known to carry plasma rifles.
During combat, Majors are usually the first ones to jump out of the Phantoms. They are known to combine their forces in battle often. The Majors will also pair up and fight together with numerous subordinate Unggoy and even Kig-Yar or Yanme'e soldiers.
Major Grunts are only slightly stronger than their lesser brothers, and are easily taken down with a headshot. In Halo: Combat Evolved, Grunt Majors could be taken out with a single headshot or a few body shots. In Halo 3, they are stronger and may require more body shots on Heroic and Legendary.
Sometimes, if a grunt major is in the battle, grunt minors will still fight after the brutes/elites leading them are dead, but this is rare. The Majors will sometimes be seen leading a small pack of Grunt Minors by themselves, but this is also rare. The presence of Grunt Majors seems to improve the Minors' accuracy slightly in Halo 3 (possibly because of the stern and almost fierce new influence the Brutes have over the Grunts). Major Grunts also throw Plasma Grenades more often than Minors.