Question: "Who was Valentinus? What was Valentinianism?"
Answer: Valentinus (AD 100—160) was an early Gnostic theologian. Valentinus was born in Phrebonis, Egypt, but moved to Alexandria as a child. He was given a Greek education and supposedly became a student of Theudas, who had studied with the apostle Paul.
History says Valentinus became an eloquent, well-known teacher in Rome. In 157 his fame made him a contender for the bishop of Rome, a position he lost to Anicetus. At that point, Valentinus left Rome, re-emerged as a proponent of Gnosticism, and developed teachings that have come to be known as Valentinianism.
Valentinus attempted to support his false teachings with the assertion that they were secret doctrines of Paul handed down to him; however, his dogmas stand in stark contrast to Scripture. For example, Valentinian cosmogony starts with a primal being, called Bythos, who in turn produced spiritual beings, the Aeons, in a higher realm. As is found in other Gnostic teachings, one of these beings made a mistake by creating the physical world, in which humanity is trapped.
For Valentinus and other Gnostics, there was no mixing of the spiritual world with the physical. Thus, they rejected the incarnation, crucifixion, and bodily resurrection of Jesus.
In Valentinianism, humankind is divided into three groups: 1) the very spiritual, who are able to accept divine knowledge (gnosis) and return to the Godhead; 2) simple believers, who, upon death, are sent to a mediocre afterlife; and 3) unbelievers, who cease to exist after death.
Valentinus’s teachings were opposed by early church defenders such as Irenaeus, Clement of Alexandria, and Tertullian, who cite him in their writings. References to Valentinianism existed only in these quotes until 1945 when the writings at Nag Hammadi were discovered. One of the works found there was a Coptic version of the Gospel of Truth. It is commonly thought that the Gospel of Truth was written by Valentinus; in fact, Irenaeus, in his Against Heresies, attributed the work to Valentinus or his followers.