A Methuselah is a Generation 4-5 Vampire in Vampire: The Masquerade. Many are thousands of years old, long enough to have interacted with their respective Antediluvian directly, and have shaped Kindred and Mortal history.
Methuselah are formidable entities, with many capable of doing feats that Modern Kindred would consider impossible to replicate. At the same time, their potency means that they can no longer feed on mortals to survive -- only the Vitae of other Kindred can sate their thirst.
Because of this limitation, Methuselah drift in and out of Torpor, frequently for millennia. Woe to the poor mid-generation or Thin-blooded schmuck to be in the immediate area of a Methuselah waking up, as they're liable to be a quick breakfast for these ancients.
Fun fact: Despite being nigh-godlike, even Methuselah are bite-sized snacks for their Antediluvians. *cough* Ravnos *cough*
V5: The Gehenna Wars
Many Methuselah are assumed to have woken up, and have rallied to the sides of their respective Antediluvians in the Middle East. The Sabbat seems to have deployed en masse to oppose them in what was soon called the Gehenna Crusade.
It's said that one in twenty vampires return from an encounter with a Methuselah, but the lucky survivor gets that sweet power boost taken from consuming Ancient Vitae.
Methuselah stand at that border where stats are essentially meaningless, as they break many NPC rules-as-written.
Even when statted, the "average" Methuselah still stands around the 500 to 600 experience point range, which makes them more than a match even for a group of Elders. Defeating one takes a tremendous amount of effort, but at least it's a somewhat more mundane challenge compared to the next step on the power level totem pole.
If having something that can use a 9-dot Clan Discipline can be considered "reasonable", that is.
Hilariously, even with how overpowered they are, they're barely considered a challenge when faced with Exalted PCs, even when using the Exalted Versus World of Darkness fan splats (which work with a much restrained powerset).