The Mother Goddess, also known as Mother Earth and Earth Mother, is a deity worshipped by the elves and, to a lesser extent, by Dwarfs and Humans who represents nature, motherhood, fertility and creation. She's associated with the birth of all life, along with the world and everything in it. There are many ancient idols and statues that represent her image scattered all over the world and in all of them she is depicted as a gloriously beautiful elf maiden with all the parts of her body associated with fertility and childbearing emphasized, like the belly and breasts. As the goddess of nature, the Mother Goddess is considered to be the one who taught elves to take care of the land and gain a plentiful harvest. She is so loved by the elves that the most devoted elven priestesses gorge themselves of food to resemble as much as possible to the representation of the goddess in the ancient idols.
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.
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 its 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.