Which Norse god is the father of Freyr and Freyja?

Njörðr is the Norse god who is described as the father of Freyr and Freyja.

Njörðr belongs to the Vanir, a group of deities associated with prosperity, fertility, nature, and the sea. He is especially connected with seafaring, wind, fishing, wealth, and fruitful crops, making him a fitting ancestor for two prominent Vanir deities.

In the surviving mythic sources, Freyr and Freyja are Njörðr’s children by his unnamed sister. The incestuous sibling marriage reflects an older Vanir tradition and is specifically contrasted with customs among the Æsir in Snorri Sturluson’s accounts.

Njörðr later becomes associated with the Æsir after the Æsir–Vanir War, when hostages are exchanged. He is also remembered for his unhappy marriage to the mountain goddess Skaði: he preferred the sea at Nóatún, while she preferred her mountain home at Þrymheimr. Baldr, Thor, and Odin are not the father of both twins.