Spoilers: Xhotl, Grymloq, and the prologue's Golden Tower. No campaign ending.

The city that is already a ruin
Xhotl, on the Lizardmen roster of 16 May 2017, is a ruin, and Kroq-Gar is its last Saurus. Mazdamundi summoned him to lead what remained of the Saurus armies and to exterminate creatures outside the Great Plan. The Last Defenders are his Immortal Empires faction, unlocked with Total War: Warhammer II. The title Last Defender of Xhotl names the lost city. It does not, on the lord page, name the settlement the campaign opens on.
The roster gives him no spellbook. His job is the fighting. Saurus Warriors are the infantry centre that can advance with him. A Skink Priest is the caster a Saurus army still has to recruit. A Scar-Veteran is the second fighter. The Geomantic Web and Blessed Spawnings are the same settled-Lizardmen tools Hexoatl uses. The lord at the front is the difference.
Every continent, on Grymloq
The 2017 roster says Kroq-Gar has fought on every continent with Grymloq. Grymloq is the Carnosaur. The mounts listed beside that claim are his own feet, a Cold One, a Horned One, and the Carnosaur. Mounting him changes how wide a melee he can reach. It also makes him a target before the Saurus line arrives, which is why the lord page tells you to advance with the infantry.
Mazdamundi remains the Slann who issued the summons. One campaign is the palanquin and the Solar-City. The other is the Saurus who was called. A military alliance between those factions in Immortal Empires is a diplomacy result. It is not the Great Catastrophe playing out again on the player's map.
The Golden Tower on the 2022 list
The 28 June 2022 prologue lists Kroq-Gar at The Golden Tower. That article's place-name is The Golden Tower. The roster's ruined Xhotl is a different name, and the two are not equated here. The prologue is a dated list from the opening of Immortal Empires, in the same sense as Hexoatl for Mazdamundi and Itza for Gor-Rok.
Gor-Rok holds Itza beside Lord Kroak. Tehenhauin preaches Sotek. Neither of those campaigns is the Last Defenders, and neither inherits Grymloq. Kroq-Gar's biography stays with the ruined city, the Carnosaur, and the summons. A province you take with the Last Defenders is the campaign's.
Kroq-Gar: gameplay and availability · More character stories
Sources
- Lizardmen army roster — totalwar.com
- Immortal Empires starting positions: a prologue — totalwar.com
- SEGA: Immortal Empires DLC Ownership Guide — support.sega.com