For those born without a sense of humour, Halopedia has an article on Grunt Ultra.
AV Johnson
This article is too damned short, Marine! You will help Gruntipedia by making it larger so it will fit the screen, fool!

Kwarsh, the Grunt king

Grunt Ultra, known as a Lucky Bastard to low-ranking Grunts, is the highest rank in the Covenant for Grunts.

After Grunts get promoted from lowly peasant to Ultra, they start to always smell like stale Food Nipple. Most Grunt Ultras have gotten their rank for actually living a long life, meaning good, healthy victims for Grunt Huffers. Like Spec Ops Grunts, Ultras never sleep, knowing that the Brutes would do stuff to them when they are sleeping. In Halo: First Strike, Ultras were seen pushing carts of lighter fluid in an Uneven Elephant. People misinterpreted this as if Ultras were some low-payed workers, But this is not true. They were just getting the lighter fluid for a party, where they would huff them and celebrate how lucky

USER Menacepotatoe steed

An Ultra Grunt using his Ultra-ness to pwn a mammoth

they were to live so long.

The only two important Grunt Ultras, or the only Grunt Ultras that are important enough to have names, is Kwarsh, the lord of all Grunts, and Bapyap, Kwarsh's best friend. 
Grunt beatdown

This guy gonna kill you. Period.

Grunt Ranks