Sad, immobilised at first, he ascended the throne (5)
I believe the answer is:
midas
But I can't explain it at all! Could you help me understand?
(Other definitions for midas that I've seen before include "One with a golden touch" , "Phrygian king" , "I'm sad (anag) -- king of Phrygia" , "Mythical king with golden touch" , "Legendary king whose touch turned anything to gold" .)