Krantt

Summary
Krantt is a Krogan term for a warrior's most trusted, those willing to kill in his name and honor. Krantt are often called for in rites or politics as a krogan's proxy and representative.

Krantt are also seen as a proof of power, as only the strongest will have warriors loyal enough to act in their name.

Shepard has the option to (temporarily) become Patriarch's and Grunt's Krantt to assist them in Mass Effect 2.

Patriarch
Shepard is sent by Aria to safeguard her predcessor as Omega's ruler from a possible hit. She wants him to force him into hiding, but Shepard has the option of becoming Patriarch's Krantt and taking out the hitmen on his behalf, restoring his status as an authority figure in Omega

Grunt
On Grunt's loyalty mission, the Urdnot Shaman queries if Grunt has any Krantt to aid him in the Rites of Passage. Shepard considers himself to match the description of Krantt as he is Grunt's shipmate and commander, but the Shaman dissmisses him and claims that the concept is completely alien to humans.