The Mother Goddess is a deity worshipped by the elves. She is so loved by the elves, that some elven women gorge themselves to look like her. She was once married to the Forgotten God. However, after catching him cheating, she wiped the memory of his existence from mortals, and banished him to the Infernal Abyss. Her appearance can be shown with her statues.
In Overlord, Goldo Golderson says, with its Dwarves, that the Goddess is a Dwarf. To prove his devotion to her, he removed the statue of the temple of Evernight and starts to build her a temple in the Golden Hills. The statue was stolen by Jewel, and finally the Overlord choose is fate.
In Overlord II, we see another feature of the worship of the Goddess: her priestesses gorge to look like her. The Goddess is considered the mother of all cute and magical creatures by the Elves, and we can see a large number of her statues at Everlight.
In Overlord: Fellowship of Evil, a statue of the Mother Goddess are visible in the museum housed by the Shining Justice in Netherdeep.