Mihirkul was most cruel king. He loved cruelty. He would make elephants fall down form high hills and would rejoice in cries of agony of the poor elephants.
Nadir Shah was another cruel king who massacred many in Delhi.
Mahraja Ranjit singh is said to have terrorized afghans so much with his cruelty that even now Afghan mothers silence their babies by saying that Hari singh Nalwa (Ranjit Singh's general) would come.
There are many others but I have referred to kings only.
i would like to add the name of Ivan 4, the czar of Russia. his cruelties even earned him the name Ivan the terrible.
