Grasulf I (died after 571) was a brother of Alboin, the first Lombard King of Italy, and possibly the first Duke of Friuli. Grasulf's son, Gisulf, is the other candidate for first Duke of Friuli. Paul the Deacon names Gisulf, but some scholars have favoured Grasulf based on a diplomatic letter which refers to him as duke.
This letter was written by Gogo, Frankish mayor of the palace of Austrasia under Sigebert I and Childebert II, sometime between Gogo's rise to power in 571 and his death in 581. It is undated and unattached to the name of either king he served. It has traditionally been assigned to around the year of his death (581), but an alternative solution put forward by Walter Goffart places it as early as 571–572 around the time of Sigebert's embassy to Constantinople. In it Gogo urges Grasulf to ally himself with the Franks to oust the infestantes (presumably the Lombards or other barbarian groups) from Italy in league with the Byzantine Empire and the Papacy. Ambassadors were waiting in Austrasia for Grasulf's reply in case he wished to delay his response to the emperor.
While the exact location of Grasulf's seat of power is unknown, if he did rule, the letter from Gogo is evidence that the "Friulian court" was capable of handling sophisticated imperial correspondence less than a decade after the Lombard arrival on Italian soil.