Marcus (Marcosian)
Marcus was the founder of the Marcosian Gnostic sect in the 2nd century AD. He was a disciple of Valentinus, with whom his system mainly agreed. His doctrines are almost exclusively known through a long polemic in Adversus Haereses, in which Irenaeus gives an account of his teaching and his school. Clement of Alexandria clearly knew of Marcus and actually used his system of mystical numbers, though without acknowledgement.
Life
Marcus appears to have been an elder contemporary of Irenaeus, who speaks of him as though still living and teaching. Irenaeus writes that the Rhone district was a home to the followers of Marcus, but appears to know Marcus himself only by his writings.The location where Marcus lived is uncertain. Given accounts of Marcus having seduced the wife of one of the deacons in Asia, and the use of Hebrew or Syriac names in the Marcosian school, the Catholic Encyclopedia speculates that Marcus must have lived in Asia Minor. On the other hand, Jerome identifies Marcus with the Marcus of Memphis who appears in the writings of Sulpicius Severus on Priscillianism.