A ruler who has almost absolute power.?

In ancient times, but it is equally true in all ages, a ruler who governs completely and also oppressively is properly described as a dictator or tyrant. While tyrants may differ from each other in particular ways (governmental and otherwise), all are similar in wielding total control of society and in making decisions based not on the good of the whole but by whim, irrationally, or simply for the sake of their own pleasure or security.