Spoilers: Character background only; no campaign ending.

Out of the Blasted Wastes
Little is recorded of Grimgor before he staggered out of the Blasted Wastes with Da Immortulz. His thirst for war is exceptional even among Black Orcs. One day without a battle fills the camp with arguments. Two days, and he smites anything he can reach, fellow Black Orcs perhaps aside. He keeps one good eye on that trouble.
Other greenskins follow the temper as well as the victories. The game's biography calls the favour Gork's. The same violence that makes his own camp dangerous is the reason a Waaagh! gathers behind a Black Orc who will not sit still.
Da Immortulz and Gitsnik
Da Immortulz are his Black Orc retinue, named because they have survived fights that should have killed them. Grimgor prefers Black Orcs. He tolerates other orcs and goblins only while there is something else to fight and they stay out of his way.
He has slaughtered a path from the Blasted Wastes to the heart of the Empire and back, then returned to Red Eye Mountain. Past the Red Eye Night Goblins, underground, Skaven numbers occupy his fury until he tires of them and strikes outward again. The axe he carries is the enchanted Gitsnik.
Grimgor's 'Ardboyz in the sandbox
In Immortal Empires he leads Grimgor's 'Ardboyz. Total War: Warhammer, the first game, is the ownership route. On the battlefield he is a Black Orc lord on foot. Waaagh! and Scrap are the faction tools around that fight. The wars after the start are the player's. They are a new campaign, not a second copy of the march to the Empire.
Azhag, Wurrzag, Skarsnik, Grom, and Gorbad lead other greenskin factions from the same broad roster. Snagla Grobspit can join a greenskin army as a hero when his pack is owned. None of them is Da Immortulz, and none of them carries Gitsnik.
Grimgor Ironhide: gameplay and availability · More character stories
Sources
- Grimgor Ironhide — wiki.totalwar.com
- The Greenskins — totalwar.com
- SEGA Immortal Empires ownership guide — support.sega.com
- A New Player Survival Guide & FAQ — community.creative-assembly.com
- Update 9.0 release notes — community.creative-assembly.com