Domentziolus or Domnitziolus was a nephew of the Byzantine emperor Phocas, appointed curopalates and general in the East during his uncle's reign. He was one of the senior Byzantine military leaders during the opening stages of the Byzantine–Sassanid War of 602–628. His defeats opened the way for the fall of Mesopotamia and Armenia and the invasion of Anatolia by the Persians. In 610, Phocas was overthrown by Heraclius, and Domentziolus was captured but escaped serious harm.

Phocas was Byzantine emperor from 602 to 610. Initially a middle-ranking officer in the Eastern Roman army, Phocas rose to prominence as a spokesman for dissatisfied soldiers in their disputes with the court of the Emperor Maurice. When the army revolted in 602, Phocas emerged as the natural leader of the mutiny. The revolt proved to be successful and led to the capture of Constantinople and the overthrow of Maurice on 23 November 602 with Phocas declaring himself emperor on the same day.