Tyrant
/ˈtaɪɹənt/
noun
A usurper; one who gains power and rules extralegally, distinguished from kings elevated by election or succession.
Any monarch or governor.
A despot; a ruler who governs unjustly, cruelly, or harshly.
Synonyms: aisymnetes, archon, basileus, tyrant flycatcher, autocrat, despot, dictator, martinet
verb
To act like a tyrant; to be tyrannical.
To tyrannize.
adjective
Tyrannical, tyrannous; like, characteristic of, or in the manner of a tyrant.