Grunt

"I don't care where I fight; as long as I get to hurt someone."

Grunt (Later known as Urdnot Grunt) is a genetically engineered krogan super soldier who appears in Mass Effect 2.

Grunt is voiced by Steve Blum. 

Krogan Berzerker
Krogan Berzerker is Grunt's class power.

Dossier
Originally, Shepard was seeking Warlord Okeer to recruit for the fight against the Collectors. But when the Commander arrived on Korlus, Okeer had completed his grand experiment: a krogan supersoldier. Unfortunately, a Blue Suns gangleader, Jedore, vented poisonous gases into the lab, suffocating Okeer to death. Shepard brought the krogan supersoldier onboard and released him from his tank. The krogan's first thought was to kill Shepard. But before it could, it desired a name. It chose "Grunt", because it was the last thing he heard from Okeer's dying words and that he considered it short and simple. Grunt relented from killing Shepard when the Commander promised him a good fight.

Lacking the sense of personal honour other members of his race hold, he is both violent and highly unpredictable. While considered by Cerberus to be reckless, unpredictable and irrationally violent, he is nonetheless considered of high value to the mission thanks to his unsurpassed physical strength and fighting prowess. In close quarters, Grunt is known to charge recklessly into the midst of his foes, though unlike more disciplined krogan fighters, such as Wrex, he may not necessarily wait for Shepard's orders before doing so.

Loyalty Mission
EDI or Kelly alerts Shepard that Grunt has become somewhat anxious, pacing back and forth in his room. Upon talking to him, Grunt will reveal his emotional state to Shepard, describing it as similar to krogan blood frenzy and being confused about how to handle it. EDI suggests visiting Tuchanka and consulting the Clan Leader there. The Clan Leader explains that Grunt is simply undergoing puberty and must take part in the Rite of Passage to prove himself as a krogan and join a clan. Gatatog Uvenk objects to allowing a tank-bred abomination to undertake the Rite, but the Clan Shaman gives Grunt permission nonetheless. Shepard accompanies Grunt to the Rite as his Krantt.

The Rite itself is a gauntlet of waves of wild fauna, including Varren, Klixen and a Thresher Maw as a boss. For the Thresher Maw you need only survive for five minutes to complete the Rite. However, killing him before time runs out earns you an achievement, respect among the krogan and a breeding request for Shepard from one of the fertile females.

Upon completing the rite, you will be confronted by Uvenk, who now seems impressed and accepting of the tank-bred Grunt. You have the options of talking him off or fighting him (or both if you have sufficient Renegade score).

Trivia

 * Unlike other krogan, Grunt's crest is a series of small bony ridges rather than a single large coloured plate. It may be that all Krogans have a similar adornment, which fuses into a plate over the course of their life, it may also be due to the fact that Grunt's DNA was cloned from ancient krogan, who may have been less evolved.
 * While performing a charge, Grunt will shout "I am KROOOOOOOOOOOGAN!".