Gaagudju was a language spoken by a primary group known by that name, and a secondary group of contiguous peoples who used it as a second language, such as the Amurdak, Gundjeihmi, Giimiyu, Bininj and Umbugarla peoples. Many of the latter ceased to speak their mother tongue in preference for Gaagudju after the 1930s, and it became in turn their first language.
The Gaagudju were a people of the northern Kakadu area. Baldwin Spencer identified the area around Oenpelli as Gaagudju territory, for they happened to be the dominant group there at the time. In Norman Tindale's estimate, the Gaagudju possessed estates covering inland of the Van Diemen Gulf some 2,300 square miles (6,000 km2) between the eastern and southern Alligator rivers, and running southwards as far as the mountain country. They were resident at both Cannon Hill and Mount Basedow.
The Gaagudju were divided into 4 estate-owning clans, the Bunidj, the Djindibi (around Munmalarri), and two Mirarr clans.
The Cobourg cattle company took up a lease for hunting buffalo in the Alligator river area 1876, and aborigines were a major part of the workforce. The Gaagudju with the arrival of the feral buffalo hunter Paddy Cahill in their area in the 1880s, were employed by the latter in tracking and harvesting kills of this Australian buffalo introduced animal. For many decade s they dominated that particular industry. There was a dramatic population collapse in that area for the next three decades (1880-1920) due to introduced diseases and new colonial land use.
Most of the material collected by Baldwin Spencer over two months on the people of Oenpelli reflects a Gaagudja perspective since Spencer's main informant Paddy Cahill happened to be fluent in that language and was an intermediary between Spencer and the three indigenous informants, Mitcheralaka (Madjirrilaaga of the Mirarr clan), Kopereiki (Gabhirrigi of the Bunidj clan, and Wardiirdi, also of the Bunidj) and Wudeirti But at the same time Spencer realized that several other aboriginal tribes were present at Oenpelli and that Cahill's Gaagudeju testimony covered their distinct traditions as well.