Gregory Thaumaturgus, also known as Gregory the Wonderworker, was a Christian bishop and theologian in the 3rd century CE. He was born around 213 CE in Neocaesarea in Pontus, in what is now Turkey, into a non-Christian family. Originally trained in law, he traveled to study under the famous Christian teacher Origen in Palestine, where he converted to Christianity. He later returned home and, around 240 CE, became the first bishop of Neocaesarea. According to later tradition, he was remarkably successful in converting the city's population to Christianity. His nickname "Wonderworker" comes from the many miracles later stories attributed to him.

His small body of surviving work provides a window into early Christian thought. His most notable writing is a farewell speech thanking his teacher Origen, which is a valuable source for understanding Origen's teaching methods. He also wrote a paraphrase of the biblical Book of Ecclesiastes, a letter on church discipline following a Gothic invasion, and a short theological treatise. His concise "Declaration of Faith" is considered significant by modern scholars for its early use of terminology that would become central to later debates about the nature of the Trinity.

Gregory Thaumaturgus is historically important as a connecting figure between earlier Christian thinkers and the later influential theologians of the 4th century. His works offer insight into the pastoral and intellectual life of a bishop during a period when Christianity was transitioning from persecution to official acceptance in the Roman Empire.