She is voiced by Saori Goto in the Japanese version.
Official description by IGA:
The 56th demon in Solomon’s grimoire. A demon with the status of a duke, also known as the goddess of the moon. Summoned by Gebel, this demon oversees one portion of the castle. She is capable of creating portals into different dimensions; once there, she can harness the power of the moon and use it to attack her enemies, firing endless crescent moon knives at her opponents. She also has a devastating gravity attack that's generated by power of the lacquer-black moon.
Gremori looks like a woman with the upper half of a human, and lower half of a camel, with the head of a camel jutting from the mid section of her body. She has eight arms, each of them embedded with a golden ring. She wears a large crown in a similar fashion to a belt, with golden chains piercing through the camel head's eyes. She also wears a white cloth to cover her chest and a white veil that covers her head, down to her eyes. Additionally, there's also an object similar to a large ring on her back, which projects the shape of a crescent moon.
Gremori (also known as Gemory, Gomory, Gemon, or Gaeneron) has her origins in the medieval grimoires. The name is possibly derived from Gimon, one of the angels of "the ninth month, which is called Kislev", from the Liber Juratus Honorii or The Sworne Booke of Honorius (dated from 13th century or earlier).
In the Lesser Key of Solomon, where she is refered to as male, she is described as a beautiful woman with a duchess' coronet tied about her middle and said to be riding on a great camel. This description appears to be tied to the images of celestial bodies, to which the summoning of spirits were linked, although how exactly is unclear. The rest of the description reads as follows: "His Office is to tell of all Things Past, Present, and to Come; and of Treasures Hid, and what they lie in; and to procure the Love of Women both Young and Old. He governeth 26 Legions of Spirits (...)."