Damocles Rowle was the second Minister for Magic, in office 1718 – 1726. He was a sadistic and cruel man. He first established Azkaban as a prison, despite the horrible effect it had on those incarcerated there. He was eventually viewed as being too “tough on Muggles” and was asked to step down (Pm).
TThe phrase "sword of Damocles" means a sense of impending doom or danger, derived from the character of Damocles in an ancient Greek story:
Damocles was an obsequious courtier in the court of Dionysius II of Syracuse, a fourth century BC tyrant of Syracuse. Damocles exclaimed that, as a great man of power and authority, Dionysius was truly fortunate. Dionysius offered to switch places with him for a day, so he could taste first hand that fortune. In the evening a banquet was held where Damocles very much enjoyed being waited upon like a king. Only at the end of the meal did he look up and notice a sharpened sword hanging directly above his head by a single horse-hair. Immediately, he lost all taste for the amenities and asked leave of the tyrant, saying he no longer wanted to be so fortunate. Dionysius had successfully conveyed a sense of the constant fear in which the great man lives (Wiktionary).