Marcion founded Marcionism, which I thought was one of the popular branches of Gnosticism, but first page Google results didn't immediately say anything like that. I think he was a student of Valentinius but idk whatever.
Bible Canon
Marcion defined a limited canon of his own in 140, hastening the need for orthodox believers to declare the canon.
He accepted Luke's Gospel, eliminating chapters 1 and 2 as too Jewish, and Paul's letters, except for the pastoral ones. In light of Colossians 4:16, he substitutes the name Laodiceans for Ephesians.
And when this letter has been read among you, have it also read in the church of the Laodiceans; and see that you also read the letter from Laodicea. (Colossians 4:16)
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the New Testament by Milton C. Fisher, Page 71.)