From Halopedia, the Halo wiki
Major, also known as Obedientary, is a Sangheili military rank. Those who hold this rank are directly superior to their Minor counterparts. Within the rank exists the Officer subclass. The Sangheili term for the Majors translates approximately as "lesser chosen" or "charged with glory".
If a Sangheili Minor proves himself in battle by killing opponents in legitimate combat, in accordance with honorable achievements earned on the battlefield, he is promoted. Sangheili do not think of promotion in the terms humans associate it with; Sangheili Minors who prove their worth to their commanders ascend to a command role. Organized under the host of Obedientaries, Sangheili Majors represent the upper echelon of the Covenant's infantry and are known primarily for their ruthlessness. Majors are some of the most skilled and experienced warriors in the field and typically command lances of fewer than a dozen soldiers, including Sangheili Minors. They also commonly pilot ground and air vehicles such as the Type-26 Wraith tank and the Type-26 Banshee attack aircraft, with the Sangheili pilots of craft such as the Seraph explicitly drawn from the host of Obedientaries. Though Majors are part of standard infantry, it is not uncommon for them to be in the presence of a shipmaster or fleetmaster, due to the critical nature of their role at the front lines. Some Majors also hold second-in-command positions aboard Covenant ships.
Officers are a subset of the Major rank. Sangheili Officers wear more ornamental armor than other Majors, though their combat role bears no apparent distinction from the rest of their grade. Like regular Majors, Officers report to their onsite Ultra or, in the absence of an Ultra, directly to their General or Shipmaster. Most Officers have a selection of units under their command, including Sangheili Minors, Unggoy, and Kig-Yar.
The Major rank and equivalent titles still see use in the wake of the Human-Covenant War. The now-defunct faction led by Merg Vol used the traditional Major rank and armor. Jul 'Mdama's Covenant instead fields Commanders, who wear a modified version of the Officer harness and helmet. During at least one engagement, Jul 'Mdama's Covenant have utilized the rank.
Typically, the armor of a Major is a standard Sangheili combat harness that is nearly identical to that of a Sangheili Minor, save for its red coloration, which is comparable to the red armor of Unggoy Majors. As with other Sangheili ranks a variety of helmet and armor styles may be utilized, though all are colored a shade of red, typically scarlet or maroon. The suit is augmented with a stronger energy shielding system than that used by Minors.
A byproduct of the Major role, Officers wear more ornamental armor, which functions with no substantial differences to Major Sangheili equipped with the standard combat harness. The officer harness features much more pronounced shoulder pauldrons and a more elaborate helmet with a backward-swept spike in the center. The design is more standardized than that of ordinary Majors, varying only in color. One color scheme is blood red with a golden tinge and brass-colored highlights; another is matte burgundy with white accents on the arms and legs, the collar, and the helmet.
Covert Major (Warzone)
In Warzone simulations, Spartan-IVs train against this type of enemy. In this simulation Covert Majors operate in very small special units. They usually lead two Sangheili Officers equipped with Type-55 storm rifles. All team members are equipped with active camouflage, and the Covert Major specifically wields an energy sword.
Sangheili Majors are commonly seen in Halo: Combat Evolved, Halo 2, and Halo: Reach (as Officers) on the Heroic and Legendary difficulties. On Easy and Normal, their presence is relatively infrequent. They commonly lead lances of Unggoy, Kig-Yar and Sangheili Minors.
Equipped with approximately 50% stronger energy shields than their lower-ranked counterparts, Majors are competent and forceful warriors capable of overpowering their opponents, namely UNSC Marines and ODSTs although not necessarily. They are less likely to perform tactical errors when compared with the inferior Sangheili Minors; Majors seek more cover and fire their weapons with a greater accuracy and faster rate of fire, and are also more maneuverable. However, they still make some tactical mistakes, as they tend not to seek cover in many occasions, even with their shields down.
There is no discernible difference between the Major and Officer: both would appear to have the same gameplay properties (i.e. energy shield strength, damage).
Halo: The Master Chief Collection
List of appearances