Supreme ruler is a term that refers to a person who has complete control and authority over a nation or a group of people. There are several synonyms that can be used to describe this term. One of the most commonly used is "sovereign," which denotes a person who has supreme power and authority. Another synonym is "monarch," which refers to a king or queen, who is the ultimate authority in a monarchy. The term "autocrat" denotes a ruler who has absolute power and authority, and who exercises it without any checks or balances. Other synonyms for supreme ruler include dictator, despot, and tyrant.