Marcion and Valentinus are roughly lumped together as types of gnostic dualism.  On the distinction between their systems see Dr. Salmon in D.C.B. iii. 820.  Marcion, said to have been the son of a bishop of Sinope, is the most Christian of the gnostics, and “tries to fit in his dualism with the Christian creed and with the scriptures.”  But he expressly “asserted the existence of two Gods.”  The Valentinian ideas and emanations travelled farther afield.