Clue: Legendary king's son is terribly pushy (8)
Answer: SISYPHUS
Explanation: Definition: Legendary king
**S**(on) **IS **+ *(pushy) 
Sisyphuys was a mythical king of Corinth, punished for his conceit by the gods. His punishment was to roll a boulder to the top of a hill every day, only to watch it roll back down again and hit him, so that he had to repeat the feat every day.