Flateyjarbók, one of the most important medieval Icelandic manuscripts
The manuscript first received special attention by the learnèd in 1651 when Bishop Brynjólfur Sveinsson of Skálholt, with the permission of King Frederick III of Denmark, requested all folk of Iceland who owned old manuscripts to turn them over to the Danish king, providing either the original or a copy, either as a gift or for a price.
The earliest mention of the name is in the Flateyjarbók (in which the spelling is 'Héri'), partly concerning the Viking age history of the Faroe Islands, written around 1380 in Iceland.
Norse sagas telling parts of the story of Augvald include the Saga of Olaf Tryggvason (by both Snorri Sturluson and Oddr Snorrason), the Saga of Half & His Heroes and the Flateyjarbok.
In Sörla þáttr, a short late 14th century narrative from a later and extended version of the Óláfs saga Tryggvasonar found in the Flateyjarbók manuscript, a figure by the name of Göndul appears and instigates the meeting of the kings Hedinn of Serkland and Hogni of Denmark and, by means of seduction and a memory-altering drought, provokes a war between the two.