Gaius was a presbyter, or elder, in the Christian church at Rome during the early third century CE. He was active during the time of Pope Zephyrinus, around 199–217 CE. Historical accounts come primarily from his theological opponent, Hippolytus of Rome, and the later church historian Eusebius. Gaius lived in a period of intense debate within the early church over core doctrines and which writings should be considered authoritative scripture.

He is known for a single work, now lost, often called his Dialogue or Disputation with Proclus. It is referenced by later authors. In this text, Gaius argued against two groups: the Montanists, a prophetic movement, and the Alogi, who rejected the Gospel of John and the Book of Revelation. Gaius himself controversially attributed these two texts to the early heretic Cerinthus, arguing they should not be part of the Christian canon.

According to modern scholars, Gaius represents a significant conservative voice in the early Roman church. His opposition to the Gospel of John and Revelation places him in a minority position against what would become the mainstream biblical canon. His debates with figures like Hippolytus are important for understanding the theological conflicts over the nature of Christ and scriptural authority that preceded the major church councils. He is remembered as a learned churchman whose views, though ultimately not prevailing, illuminate the diversity of thought in early Christianity.