a principal formulator of Eastern Gnosticism, a system of religious dualism (belief in rival deities of good and evil) with a doctrine of salvation by gnōsis, or esoteric knowledge.

From the scant data available, Theodotus is known to have taught Gnosticism in Asia Minor c. 160–170, elaborating on the principles of the early-2nd-century Gnostic leader Valentinus. Theodotus' teachings, of primary importance for the study of primitive Gnosticism, survive in Excerpta ex Theodoto (“Extracts from Theodotus”), actually a scrapbook that the 2nd–3rd-century Christian philosophical theologian Clement of Alexandria appended to his Stromata (“Miscellanies”). Certain passages integrate the comments of Clement; thus, the unsystematic arrangement of the material causes problems of interpretation.

Essentially, the Gnosticism of Theodotus affirmed that the world is the product of a process of emanations, or radiations, from an ultimate principle of unconditioned being or eternal ideas. Intermediate beings in this hierarchy of perfection include God the creator of matter and Christ the redeemer, who united himself to the man Jesus at his baptism to bring men gnōsis. Salvation, he concluded, is reserved for Gnostic believers infused with pneuma (“spirit”).

Theodotus further developed the role of the inferior spiritual beings, or angels, and their relation to Christ. He mentions a Eucharist of bread and water and anointing as a means for release from the domination of the evil power.