One of the rebel kings at the beginning of Arthur’s reign. A variation of Yder used by Malory, who calls him the king of Cornwall.
When the Saracens attacked Wandesborow Castle, forcing the rebel kings to suspend their war against Arthur, King Idres with four thousand men of arms was put into the city of Nauntes in Britain
to watch both the water and the land.
Source
Le Morte Darthur | Sir Thomas Malory, 1469-1470