Wikipedia
The Guduscani or Guduscans were an indetermined tribe around present day Gacka ( Lika), between upper Kupa river and the Dalmatian coast, or the inhabitants around the river Guduča near Zadar, a Croatian tribe, i.e. the people of the Bribir region. It has been assumed, that they were part of the Vandals, Goths or Croats. However, the view that the Guduscans were Goths is not widely accepted, their state was in Italy and it ceased to exist in the 6th century, while their presence in the former Roman province of Dalmatia was not dominant. The German historian Josef Baptist von Weiß (1820–1899) thought that the Guduscani were descendants of the East Germanic Vandals.
In the Frankish Annals, the Guduscani are mentioned as allies to the Carolingians, the Duke Borna is mentioned as "dux Dalmaciae", "dux Dalmatiae et Liburniae" and "dux Guduscanorum". Borna was first titled duke, i.e. prince (dux) of Guduskani/Guduščani, which indicates that the Guduscans could have been the basis of Borna's authority and could have occupied a much larger territory from Bribir to Gacka, including the coastal area.
In 818 they were part of an envoy of Borna sent with the South Slavic tribe of Timočani to the court of Louis the Pious in Herstal. In 819 Ljudevit Posavski conquered their lands and pushed Borna to Vinodol.
They were part of the army of Borna against Ljudevit Posavski at the Battle of Kupa but deserted before the battle. Borna conquered their lands again upon returning from the battle.
Constantine VII Porphyrogennetos (905–959) mentioned in his work De Administrando Imperio a županija in Croatia in the 10th century called "Gūtzēkă", which is translated as Gacka. Some tried to connect Gacka as an ethnonym of the Guduscans, but it is not certain that Gacka got her name from the tribe.