A theologian is generally understood to be a person who teaches or is educated in theology. Its root form, theology, is derived from the Greek θεολογία (theologia), from θεός (theos, god) and λόγος (logos), with the suffix ια (ia, "state of," "property of," "place of"). A literal translation of the Greek word would be "to talk about God." Evagrius Ponticus wrote that "If you are a theologian, you will pray truly. And if you pray truly, you are a theologian." (Treatise On Prayer, 61).

Theologians use various forms of analysis and argument to help understand, explain, test, critique, defend, or promote religious topics. Theology had its origin in classical Greek thought, but was given new senses within the Christian context as the Fathers of the Church.