A usurper; one who gains power and rules extralegally, distinguished from kings elevated by election or succession.
A despot; a ruler who governs unjustly, cruelly, or harshly.
A villain; a person or thing who uses strength or violence to treat others unjustly, cruelly, or harshly.
Any person who abuses the power of position or office to treat others unjustly, cruelly, or harshly.
The tyrant birds, members of the family Tyrannidae, which often fight or drive off other birds which approach their nests.
Tyrannical, tyrannous; like, characteristic of, or in the manner of a tyrant.