Spoilers: The pact in the character biography. No campaign ending.

Who he is in Total War
Kemmler leads The Barrow Legion for the Vampire Counts. Total War: Warhammer unlocks him. The Grim and the Grave is Ghorst’s pack, not his. In battle he is the caster. Update 9.0 makes Krell a unique agent, gives Kemmler Invocation of the Lichemaster to summon Cairn Wraiths, and gives him Eternal Vigour for allies nearby. Skeleton Warriors hold a line so the necromancer can keep casting.
The Aye-Aye patch of 2018, written for Mortal Empires, moved him out of a shared Vampire Counts faction and sat the Barrow Legion at Blackstone Post, the new province capital of the Northern Grey Mountains, bordering Bretonnia. That sentence is the patch’s campaign move. It is a Mortal Empires start. It is not an Immortal Empires settlement name, and it is not a chapter of the Grey Mountains biography.
Power, the Grey Mountains, and the mound
The Total War Wiki biography opens on power sought for its own sake. Kemmler studied necromancy from his youth until his command of it was rarely matched. He defiled ancient tombs for what they held. Rivals then engineered a defeat that broke his body and his mind. Half-sane and disfigured, the man who had called himself Lichemaster wandered the Grey Mountains as little more than a beggar.
The same biography brings him, guided by forces it does not name, to the burial mound of a once-great Chaos champion. There he struck a pact. The gods would restore his health and return power greater than he had lost. He would do their bidding. The biography stops on that bargain and on the fear the Lichemaster’s name still carries. It is Warhammer Fantasy background printed for the game. A player’s Barrow Legion war is another campaign on top of it.
Krell and the other counts
Krell enters with the unique-agent change in update 9.0. The biography of the mound and the pact does not use his name. Treat the agent as the game’s fighting companion for the Lichemaster, and the pact as the biography’s account of how the beggar became dangerous again. They sit side by side. One is not a retelling of the other.
Vlad and Isabella share Sylvania. Mannfred studies and rules through the Drakenhof Conclave. Ghorst’s caravan is the other necromancer’s campaign. Neferata works through the Lahmian Sisterhood. Nagash can name Mortarchs. Kemmler’s page stays with the Lichemaster, the Grey Mountains, Blackstone Post as a 2018 Mortal Empires start, and the Barrow Legion you actually play.
Heinrich Kemmler: gameplay and availability · More character stories
Sources
- Heinrich Kemmler — Total War Wiki — wiki.totalwar.com
- Announcing the Aye-Aye! Patch — Total War — totalwar.com
- Update 9.0 release notes — Total War — totalwar.com
- Immortal Empires DLC Ownership Guide — SEGA — support.sega.com
- Immortal Empires DLC Ownership Guide — SEGA — support.sega.com
- Update 9.0 release notes — CA — community.creative-assembly.com
- Lords of the End Times: Free-LC | Neferata — CA — community.creative-assembly.com