1439, Mercurian and Narayan lure the master vampire of their family line into their home with the promise of a truce. They come across as so convincing, the vampire in question falls for it, and is most viciously attacked by the Steeles and their friends, and left to die tied to the roof of a house. Not in any way having expected such maliceous acts (vampires just didn’t hurt vampires back in those days), there is nothing to save him, and he dies at sunrise.
Later that year, the Immolators Guild is founded by Narayan and Mercurian Steele, one of the first proper clans of the time, numbering a full five members, namely those involved in the killing of the master vampire - and they base the entire clan philosophy and it’s efforts on defence from exactly such acts, should they ever be plotted against them.
Accordingly, they have worked towards taking the vampiric immortality one step further to absolution - where before, the sun was their foe, now the Steeles are daywalkers, since roughly a century and a half. It is their greatest achievement, but they keep quiet about it mostly, and the powers such immortality may open up are unused. They have no interest in city domination - their wish is one of survival, not of destruction.