The Vulgate VII names a 'Helyes li chatelains de Roestoc'. He appears to be one of the rebel kings, possibly killed in battle. The Lady of Roestoc is his widow or daughter.
Helyes of Thoulouse
Elias; Helyes li Toulousans, - nes de Toulouse
Helyes had enough knowledge and power to call up at least one wonder, and might have performed miracles had he chosen to study along those lines. Galeholt persuaded Helyes to tell him how long he had still to live.
Helias of Toulouse | The Legend of King Arthur
This little book could have enabled Helyes of Thoulouse to perform miracles, had he cared to study it. On at least one occasion, he used it to conjure up an apparently demonic apparition to help elucidate a prophecy concerning Duke Galeholt's term of life.
None of Galeholt's other clerks had success when they tried to consult this book; perhaps they were not learned enough.