The origins of the being known as Mayoor are shrouded in mystery.  At some indeterminate point in the past, he battled Nabu and was imprisoned in a tomb in the Yucatan.  Mayoor is referred to as a Mayan 'god" but contemporary references describe no one named "Mayoor" in Mayan mythology, suggesting he may have had other names or been an imitator. He resembles Ah Puch, the Mayan god of evil, though any connection between them is purely speculative.

Centuries after their initial encounter, Nabu was incarnated as Doctor Fate, a prominent mystery man of the 1940's.  In late 1940, Mayoor's temple is happened upon by explorer Bill Credon.  When he draws close to the tomb, Mayoor compels Credon to pull an iron ring, freeing the ancient sorcerer enough to dominate the explorer. Mayoor tells Credon that Inza Cramer hold enough mystical knowledge to be his agent on Earth, allowing to rule over its people.
 
In the Spring of 1941, Inza is taking a Caribbean cruise that brought her close to the Yucatan Peninsula.  She meets a fellow passenger who is Bill Credon, who claims to have seen a monster in the depths of the Mexican jungle.  He offers to share his exploration with the curious Inza, who accepts.  As the enter the jungle on horseback, Inza begins to feel uneasy.  Credon points out a temple and when they enter, Inza falls under the spell of a horrifying statue. 

Meanwhile, her proximity is freeing Mayoor from his tomb and he uses his magic to telepathically communicate to Dr. Fate, taunting him that he will soon be free and that Inza is almost in his grasp.  After taunting Fate, Mayoor turns his attention back to Inza who he torments and displays his power by lifting his temple into orbit.  When he returns it to the Mexican jungle, Inza exclaims that only Fate can save her but Mayoor claims perhaps not.

Meanwhile Fate casts a spell of magic darkness against which evil will be illuminated. Searching the globe, Fate eventually finds Mayoor's temple despite the sorcerer's best efforts.  Mayoor starts by be threatening Inza  but is astonished when Fate says the world is more important.  He then pleads for his liberty but Fate refuses.  Before he can act, Fate ignites his body and he falls into a deep crevasse beneath his temple, presumably to his destruction.  When Fate and Inza leave the temple, the find Bill Credon dead, his life evidently tethered to Mayoor (More Fun Comics #64).

Whether Mayoor was truly destroyed remains unknown.  A vision of Mayoor was conjured by the Psych0-Pirate and Fate seemed unsurprised that Mayoor was alive, suggesting there may have been more encounter with the Mayan demi-god (Showcase Comics #56