dictator; despot
Refers to a ruler with absolute power, often with negative connotations of oppression.
その国は長年独裁者に支配されていた。
That country was ruled by a dictator for many years.
独裁者は反対意見を一切許さなかった。
The dictator did not allow any dissenting opinions.
Compound of 独裁 (どくさい, 'dictatorship, autocracy') + 者 (しゃ, 'person'). 独裁 is from 独 (alone) + 裁 (judge, decide).