The concept of an Ogdoad appears in Gnostic systems of the early Christian era, and was further developed by the theologian Valentinus (ca. 160 AD).
The number eight plays an important part in Gnostic systems, and it is necessary to distinguish the different forms in which it appeared at different stages in the development of Gnosticism. The earliest Gnostic systems included a theory of seven heavens and a supercelestial region called the Ogdoad. Astronomical theories had introduced the concept of seven planetary spheres with an eighth above them, the sphere of the fixed stars.
In the system of Valentinus, the seven heavens, and even the region above them, were regarded as but the lowest and last stage of the exercise of creative power. Above them was the Pleroma, where were exhibited the first manifestations of the evolution of subordinate existence from the great First Principle.
All the early Gnostics of whose opinions Irenaeus gives an account, in a section () probably derived from an earlier writer, agree in the doctrine that the world was made by the instrumentality of archons (angels). The brief account given of the teaching of the first two in the list, Simon and Menander, does not state whether or not they defined the number of these archons; but it is expressly told of the third, Saturninus (), that he counted them as seven. At the end of the first book of Irenaeus is a section to all appearance derived from a source different from that just referred to. He here () relates the opinions of heretics to whom he himself gives no title, but whom his copyist Theodoret (Haer. Fab. i. 14) calls Ophites. The Ophite teaching may be used to illustrate that of Saturninus, his connexion with that school being closer than with any other. It would have been natural to think that the number of seven archons was suggested to Saturninus by astronomical considerations; and this supposition is verified by the statement in the later chapter () that the holy Hebdomas are the seven stars called planets. In fact, the sphere of the seven stars, Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon, were supposed to be presided over, each by a different archon. Their names are differently given; Irenaeus (c. 30) giving them, Ialdabaoth, the chief, Iao, Sabaoth, Adonaeus, Eloaeus, Oreus, and Astaphaeus. With this closely agrees Origen, who, writing of the Ophites (Adv. Cels. , ), gives the names Ialdabaoth, Iao, Sabaoth, Adonaeus, Astaphaeus, Eloaeus, Horaeus. Epiphanius (Haer. 26, p. 91), relating the opinions of what was clearly a branch of the same school, places in the highest heaven Ialdabaoth or, according to others, Sabaoth; in the next, Elilaeus according to one version, Ialdabaoth according to the other; in the next Adonaeus and Eloaeus; beneath these Dades, Seth, and Saclas; lowest of all Iao. It was thought that each of the Jewish prophets was sent by a different one of these seven archons, whose special glory that prophet was to declare. Thus () the first archon sent Moses, Joshua, Amos, and Habakkuk; the second Samuel, Nathan, Jonah, and Micah; the third Elijah, Joel, and Zechariah; the fourth Isaiah, Ezekiel, Jeremiah, and Daniel; the fifth Book of Tobit and Haggai; the sixth Micah (qu. Malachi?) and Nahum; the seventh Ezra and Zephaniah.