Tremere

Ah, the Tremere, a.k.a. Rein·Hagen's pet Tremary Sues. 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.

Genesis

When designer Mark Rein·Hagen decided to include a clan of thaumaturges in his new Vampire game, rather than utilize a vampiric clan that had millennia to perfect blood magick as simple logic would have dictated, he instead opted to myopically shoehorn his pet Tremere mortals from his previous Ars Magica game as a new vampire clan with a historically absurd monopoly on thaumaturgy, which made them an entire clan of Mary Sues ("Tremary Sues"), hated both in-game and out-of-game by players of every other vampiric clan, especially the clans that have a much better narrative justification for thaumaturgic mastery.

Overview

In-game 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 (actually a common misconception. The Technocracy didn't even exist yet. Tremere was just kind of shit at magic). 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 the Salubri, elevating them to legitimate clan status. Tremere then immediately fell into torpor, as the entire kindred community collectively took a step back and said "wait, what the fuck?", as the Tremere began to launch a systematic purge of the Salubri across the entire world, to this day leaving them decimated to the point of no return.

Since then, they have concocted an awful form of magic; Thaumaturgy, even though it is much more similar to Blood Magic in practical terms. Whilst Tremere have proved themselves to be slimy fucks supreme, they have made deals with literally every clan to the point where even if they wanted to, they would not be able to wipe the Tremere out.

The Man Himself

Tremere himself has been constantly mutating and changing shapes since he fell into torpor, taking shapes such as an enourmous worm whilst writhing and wriggling around. Unbeknownst to everyone, the spirit of Saulot had decided to not take things easy on this usurping little upstart, attempting to possess him. Eventually, at some point around Gehenna, Saulot won, leaving Tremere to possess the body of Goratrix, leader of the Tremere Antitribu.

Mage: The Awakening

The name and general spirit of the Tremere continue into the New World of Darkness. The Tremere Liches are a Legacy of, well, liches in Mage: The Awakening. They still have the theme of undead wizards willing to violate the souls and lives of others for magical power. While initially a small Legacy, they've since grown into an Order in their own right. Even other evil magi hate them and want them dead. They are also, notably, not actual vampires, and thus don't interact too terribly much with the Kindred of Vampire: The Requiem (although they apparently have some pen pals in the Ordo Dracul)