Forseti (Old Norse "the presiding one", actually "president" in Modern Icelandic and Faroese) is the Æsir god of justice, peace and truth in Norse mythology. Fosite is a god of the Frisians often identified with Scandinavian Forseti. So Jacob Grimm, Teutonic Mythology, who takes forseti "praeses" as the original meaning, postulating an (unattested) Old High German equivalent forasizo. Grimm notes that the god's sanctuary at Heligoland would have made him an ideal candidate of a deity known to both Frisians and Scandinavians, but has to admit it is surprising that he should remain entirely unmentioned by Saxo Grammaticus.
Forseti was considered the wisest and most eloquent of gods of Asgard. In contrast to his fellow god Tyr, who presided over the bloody affairs of carnal law, Forseti presided over disputes resolved by mediation. He sat in his hall, dispensing justice to those who sought it, and was said to be able to always provide a solution that all parties considered fair. Like his father Baldr, he was a gentle god and favored peace so all judged by him could live in safety as long as they upheld his sentence. Forseti was so respected that only the most solemn oaths were uttered in his name.
He is not mentioned as a combatant at Ragnarok, so it is assumed that as a god of peace he abstained from battle.
It is said that after gathering laws from all the regions, they embarked on a sea voyage to a remote place where they could safely discuss the process of compilation. However, a vicious storm arose and while at the mercy of sea they invoked the name of Forseti to save them from peril. They noticed that a 13th person appeared in the boat and safely led it to a deserted island. There, the person (presumably Forseti himself) split the earth and a spring was formed. Having consecrated the place he dictated the unified code of laws that merged all the best regulations of various local laws and suddenly vanished.
The island became a place of worship to Fosite and the spring was its holy place. The island's integrity was respected by all Norsemen and no warrior dared to make a raid there in fear of the punishment that would result in being cast down to the kingdom of Hel rather than upwards to Valhalla. All major legal assemblies gathered at the island. The disputes were undertaken in the light of day only, and never in winter as it was believed that darkness was anathema to truth and just resolve.
"Fositesland" is mentioned by Alcuin as in confinio Fresorum et Danorum. Adam von Bremen identifies the "Fosite island" with Heligoland. Fosite has been suggested to be a loan of Greek Poseidon into pre-Proto-Germanic, perhaps via Greeks purchasing amber (Pytheas is known to have visited the area of Heligoland in search of amber).