Unggoy Ultra

Unggoy Ultra is the highest known Unggoy rank.

Rank
The Grunt Ultra is the highest Unggoy rank seen so far in the Covenant military. Like Sangheili Ultras, Grunts Ultras wear distinct white/pearl-like armor.

Grunts Ultras can sometimes be seen commanding groups of lower class Grunts in battle, and are even seen leading black-armored Special Operations Grunts into combat, and it is rare for the player encounter them when playing on lower difficulties, such as Easy or Normal (without the Thunderstorm Skull activated). If the Thunderstorm skull was activated, all grunts that are fought will be Grunt Ultras.

Unlike Elite Ultras, Grunt Ultras do not appear to have any immunity with their command. It is just as likely that two or three will be encountered leading a small group of Grunts, yet the Elites, (or Brutes in the Loyalists) are ultimately in complete command; similar to the way that even Minor Prophets outrank Sangheili Ship Masters.

These Grunts, like their lower-ranking cousins, appear in groups. They are very intelligent, making as few tactical errors as Major Elites. They usually display even more bravery in combat than a SpecOps unit, and are more often used for specialized attacks, rather than generic military operations.

Combat
Grunt Ultras usually throw more grenades and are far more accurate and deadly at a greater distance than the lower ranked Major and Minor Grunts. They also wield Needlers with greater frequency than their inferiors, though it is still common for them to use Plasma Pistols, which they will overcharge. They can also take the same amount of damage Spec Ops Grunts do (more than three times as much as a Grunt Minor can), but they are still vulnerable to headshots (even though it may take more than one for lower-end weapons). Like SpecOps Grunts, they are rarely caught sleeping on duty. They still panic if they know that they are being overwhelmed, but are more likely to go berserk than panic - especially if one of their comrades was killed by a grenade.

A Grunt Ultra, compared to an average Minor Grunt, can take much more damage and usually takes two to three melees instead of one to be killed, even on lower difficulties like Normal. Even on lower difficulties Ultras can still survive a headshot on account of their helmets.

Background
The purpose of this rank designation has been generally unclear. They were first mentioned in Halo: First Strike, pushing carts of cleaning fluid, demonstrating that they still hold very low positions despite the title of "Ultra." However, they were also seen inside the Scarab walker in New Mombasa along with high-ranking Elites (Minor, Major, and Ultra). They were also seen throughout New Mombasa, Delta Halo and Cairo Station. This led some to believe that they were "technicians" or engineers (not to be confused with the Engineer species) of some sort, but the production book, The Art of Halo, confirms that they outrank Grunt Majors. It has, however, been suggested that white armor actually signifies manual labor, while the more silver armor signifies Ultra. Still, there is not a sufficient color difference to make this a significant case. It is likely that even though they are high-ranking Grunts, they are not free from manual tasks.

The rank is a rare achievement for an Unggoy, due to the fact that the species has a high death rate. Grunt Ultras most likely delegate a great degree of respect from the Grunts under their command, as their combat powers must be exemplary - or they are just extremely lucky.

Trivia

 * If one plays Halo: Combat Evolved with an unsupported video card, but has at least 32 megabytes of video memory, all armor colors will be white, with some exceptions such as the Hunter, which has led to some fans thinking that all the Grunts in Halo: Combat Evolved are Ultras. However, white is the basic color of all models in the Halo: Combat Evolved engine. The models are rendered with no specific color until they are selected by an algorithm that determines which Grunt variant to spawn, determined by the difficulty level (meaning higher difficulties are more likely to spawn Grunt Majors). There is a degree of randomness involved, as the player might notice a Grunt Minor in one location die, then realize that it changes to a Grunt Major. This is most noticeable when viewing maps with SparkEdit, a modding program. It renders all models based on their constituent bitmaps; the game engine adds the lighting effects and determines which variant to spawn when that part of the level is played. In SparkEdit, all models, except Hunters and Marines, have white armor, including Spartans.
 * In Halo 2, if the Thunderstorm skull is activated, all Unggoy will be upgraded to this rank.
 * In Halo: Reach, Ultras have a cylindrical methane tank and a full face mask. The shape of the methane tank appears to have been influenced by early concept art for Halo: Combat Evolved, and designs later seen in the Halo Graphic Novel, Halo: Uprising, and Halo Wars. They have been nicknamed "Keg Grunts" by Bungie due to the shape of the methane containers.
 * In Halo: Reach, it is possible to shoot an Ultra's helmet off its head without killing the Grunt. This is required if the player is intending to kill it with a headshot.
 * The helmet worn by Unggoy Ultras in Halo: Reach bears a remarkable resemblance to the Death Mask from Mass Effect 2.