Lost to the mists of time, Slaughter was an ancient Decepticon warrior. His tale was recounted by the sage Alpha Trion who possesses his signature weapon, a massive sword. Evidently much of his core programming was encoded onto the sword, giving it somewhat of a will of its own long after Slaughter's demise. As a result the weapon is as close as a technological item can manage towards being cursed, requiring of its wielders a potent mental fortitude to avoid being overwhelmed by it and forced to pick up Slaughter's work where he left off.
Whether or not Slaughter's core programming was able to suborn even Alpha Trion is up for debate, but certainly something about the old Autobot isn't quite right. It is likewise unknown whether the sage encountered the sword prior to reaching Axiom Nexus on his own homeworld, or whether Slaughter (or simply his sword) were amongst the transdimensional flotsam that washed up at the multiversal crossroads.