Where does “कठमुल्ला” come from?

कठमुल्ला (Hindi) comes from Hindi मुल्ला, from Arabic مُلَّا, from Classical Persian ملا, from Arabic مَوْلَى — vicar, guardian; lord; Lord.

कठमुल्ला (Hindi): an ignorant person; one falsely claiming to be knowledgeable; a bigot