Tremere

Ah, the Tremere. Hated by all and loved by none, these guys are the vampiric equivalent of the Marines Malevolent, mainly due to how sheerly despised they are amongst most of the Vampire community. So why are they hated so much? Because they are Tzeentch-tier scheming dickwads that weren't even originally vampires that have made themselves indispensable.

Originally a House of Mages in the Order of Hermes, House Tremere was one that quickly began to realise that their magic would stop working due to the advancement of the Technocracy. This meant a lot to them, because if the magic went, so would their immortality potions that had kept them around for so long. So, they began to look for solutions; rituals, incantations, and other such wizardy shit before Goratrix, an elder, discovered the solution; Vampirism!

And so Tremere, the house's founder and namesake, and six other elders were summoned to Goratrix to become Vampires. This meant, however, that they lost their magical powers and avatars, which obviously bummed them out a lot. The other clans, particularly the Tzimisce, would make war against the Tremere, treating them as third-class citizens and generally not taking these upstart little shitwizards seriously.

So, on a quest to make others respect them, they did the unthinkable; Tremere diablerised Saulot, motherfucking Antediluvian of Clan Salubri, elevating them to legit clan status. Tremere fell into torpor, as everyone collectively took a step back and said "wait, what the fuck?", as the Tremere began to make awful shitwizardy blood magic rituals and creepy gargoyle vampires.

Since then, with said awful blood magic, the Tremere have proved themselves to be slimy fucks supreme, making deals with literally every clan to the point where even if they wanted to, they would not be able to wipe the Tremere out.