Marcion of Sinope
Valentinius was among the early Christians who attempted to align Christianity with Platonism, drawing dualist conceptions from the Platonic world of ideal forms ("pleroma") and the lower world of phenomena ("kenoma"). Of the mid-2nd century thinkers and preachers who were declared heretical by Irenaeus and later mainstream Christians, only Marcion of Sinope is as outstanding as a personality. The contemporary orthodox counter to Valentinius was Justin Martyr, though it was Irenaeus of Lyons who presented the most vigorous challenge to the Valentinians.