Catharis, Matron of Crucibles, is a Super Unique Death Maiden found in the Noble's Rest Courtyard in Diablo III. She appears during the Souls of the Dead quest.
She is operating the Master Soul Crucible, the largest one in Westmarch. Initially, she is shielded from harm, and only becomes vulnerable when all six corpse piles are destroyed.
In combat, she has Fast and Electrified affixes, and in addition attacks with hordes of Reapers, which are summoned both by herself and by the crucible. If players feel overwhelmed, she can be kited to the back of the row and killed with relative ease.