During the decline of the Western Roman Empire, various Germanic tribes that had been settled as 'foederati' or federates effectively took over swathes of Roman territory, being settled in these regions while the area was still de facto Roman territory. The Visigoths, Burgundians, and Odoacer of Italy ruled as de jure viceroys of the Roman Emperor, with the Visigoths formally renouncing this is 475AD. In Odoacer's case, he ruled in Italy until he was overthrown by Theodoric, King of the Ostrogoths, in 493AD, who continued the pretence of merely being a viceroy for the Eastern Roman Emperor. However, this legal fiction can't have been retained over the whole of the Ostrogoths' rule in Italy, as the later Emperor Justinian I saw fit to invade and conquer Italy in 535AD (the year after finishing off the Vandals in Africa). So my question is, when was this legal fiction of Roman rule in Italy ended?
"Pretense" and "Fiction" are certainly the right words for it. Nobody really bought into it at the time (except the Roman Senate, at knife-point), and I wouldn't suggest we do so now.
The ruler of the Eastern Roman Empire Zeno made it clear he felt Julius Nepos was the rightful ruler of the West until his death in 480. He didn't accept Odacter or his puppet Western Emperor, but there wasn't anything he could do about them immediately. Eastern resources were fairly well consumed keeping their own borders guarded and bribing their own German tribes.
As far as the Eastern Empire was concerned, Julius Nepos was the Western Emperor from 474 to 480 (although for the last 5 years, he only actually controlled a bit of Dalmatia), and after that, there never was another one. Odacter was never really accepted by them as anything but a fait accompli, and Theodoric's status entirely relied on the fact that he initially invaded Italy with Eastern Emperor Zeno's encouragement.
There was really only one Ostrogothic ruler after that*, Theodoric's grandson Athalaric. His death in 534 set off a chain of events that saw the Ostrogothic kingdom at war with The Eastern Empire the next year, which ended with Rome (re?)taken for Emperor Justinian.
* - OK, technically there were three more, but they all spent their entire rule losing their territory to the armies of the Eastern Roman Emperors