Not much is known about Forseti as he is only mentioned twice in Old Norse literature. Our main source is from the Poetic Edda. The first mention of him is in the 15th stanza of the Grímnismál or “The Song of the Hooded One”, part of the aforementioned Poetic Edda. The Poetic Edda is a collection of poems by anonymous Old Norse-speaking poets collected by Snorri Sturluson. Sturluson then took the information in the Poetic Edda and extrapolated it into the Prose Edda. The debate about the authenticity of the Prose Edda has been raging amongst scholars for some time. For example, the second mention of Forseti is in the Prose Edda, where Sturluson’s claims he is the son of Baldr and his wife Nanna. However, this is questioned by some scholars as there is no basis for this except Sturluson claims. Despite this, most sources do call out Baldr and Nanna as Forseti’s parents.
The name Forseti is thought to come from the word for “chairman”, “presiding” or “president”. Other translations indicate it is from the words for “winding stream” or “cataract”, since he may have been first worshiped by the sea faring peoples of Frisia as Fosite. As expected for a god whose name means “Chairman” or “President” in Old Norse, Forseti’s forte was mediation and law. He was the divine inspiration for a “lawspeaker”, or lögsögumaðr in Old Norse, which was the head of the þing, or Scandinavian legal assembly. The lawspeaker acted as judge and decided the verdict of disputes in accordance with the law. He decided both disagreements between the gods as well as thorny disputes among humans. It is said that no one who came to him for justice went away unsatisfied. His hall was called Glitnir or shining as its silver roof and gold pillars radiated light for miles around. His symbol was the golden axe he carried. Forseti was also famed for his ability to meditate, which kept his mind clear and peaceful so he could deliver judgements with out emotion.
The Frisian connection is disputed. One of the main sources we have for it is the 8th century account of the life of St. Willibrord. In the blindingly obviously named Life of St. Willibrord, the author discusses the saint visiting an island between Denmark and Frisia, where there was a spring holy to Forseti. Because of its innate holiness, all water gathered there was done in silence. There is another reference to this Frisian spring in a medieval account, where Frankish king Charles Martel told twelve Frisian law-speakers they had to conform to his laws or face punishment. The choices were slavery, death or being cast adrift in a rudderless boat on the ocean. They picked option three, and were put in a rudderless boat and sent on their way. The twelve men prayed to the Christian god to save them. In answers to their prayers, a thirteenth man carrying a golden axe appeared in their boat. He used the axe as a rudder and led them to the island, then used the axe to split the land so a spring appeared. He told the men he was Forseti and proceeded to teach them all the laws they needed to know then disappeared. The shrine was apparently in use until St. Willibrord shut it down. I get that they were converting folks to Christianity, but that strikes me as a buzz kill.
Echoes of his legacy are seen in that the Icelandic word for “president” is “forseti”. Another Nordic name, Veseti, is also supposed to have roots in Forseti as it means “person who is incharge of or presides over the hallowed space , or ve”.