Norse Mythology: Possibly an older version of Njord (as the opposite sex) since scholars say their names are linguistically related, or his sister with whom he has Frey and Freya -- Leach states Ingun is their mother.
Tacitus in 98 CE describes the worship of Nerthus by the Danish. He calls her Mother Earth and relates the ritual surrounding her. According to Tacitus, Nerthus' sanctuary was in a sacred grove on an island and within the copse was a cart under a covering. When the goddess came to her sanctuary the priest was aware of it and would walk alongside her cart pulled by cows as Nerthus visited places. While the goddess was among people no war was allowed and all weapons were put away. Once the goddess was brought back to her shrine, she, her cart, and its covering, were all washed in a lake by slaves. The slaves were supposedly swallowed by the lake afterwards.

(Nicole Cherry, A list of Norse Beings,