The celestial triumvirate said to be older than any god or cosmic entity make their home within the God Quarry at the fringes of the Universe. When the divine either lose their following are are whethered enough by time, this coven of enchantresses appear before them to be spirited away towards their domain. Entrapping said beings within their quarry pit redistributing their cosmic essence back into the universe.
The Witches of Infinity were created by Jeff Lemire and Mike Deodato Jr. Appearing in Thanos #4 (2017) and then being named in Thanos #8 by Thanos himself.
As he took up the reigns of his former masters interstellar empire, Corvus Glaive enlisted the aid of the witches against his former partner Ebony Maw and his new Black Vortex empowered protege; Thane. The three summarily stripped the son of Thanos's powers leaving him mortal before disappearing.
It was unknown as to what Corvus had bartered with them to act on his behalf. When next seen the Witches sat within their domain at the God Quarry resting in a Black Hole. The three were beset by the brothers of Titan Thanos and Eros, while they only scoffed at the now mortal warlord who made demands of them. They became incensed enough at Starfox's attempt at manipulation, that they aged him into and old crone in response.
Once upon de-aging him as a sign of humbling. The sisters bade Thanos to step within the graveyard of fallen gods they oversaw in order for him to begin his ascension, once inside and assimilated into the quarry. All they and his brother could do was watch and wait as none had ever come & gone from it before.