I do not remember exactly when, but once a gothic magister militum tried to usurp and most probably to implement a similar governement (puppet emperor) like in the west. Luckily the plebs of Constantinople has beaten the Goths in bloody street fights. The WRE was less lucky. Due to the move of the capital to Mediolanum and later Ravenna there was no plebs and no senate to support the emperor anymore and the foreign magistri had an easy job. One of many major differences why the East did not fall. The role of the plebs of Rome is widely underestimated.
I think you are thinking of the enemy of Stilicho in the east, who happened to be Theodosius' right hand man in Constantinople no? Either him or Aspar?
The guy you two are thinking of was Gainas the Goth. He tried to take advantage of magister militum Leo's lack of success. So he was appointed and didn't do any better, but blamed it on the Empress Eudoxia and essentially tried to mount a coup. Until the residents of Constantinople tore his troops apart limb from limb.