Which bishop is known for opposing Marcion's teachings?

The bishop known for opposing Marcion's teachings is Tertullian. He was a significant early Christian author and theologian who vigorously criticized Marcion's beliefs, particularly his view of the Old Testament and the nature of God.

Tertullian argued against Marcion's dualism, which posited two gods: a vengeful creator god of the Old Testament and a benevolent god of the New Testament. He emphasized the unity of God and the coherence of scripture, asserting that both the Old and New Testaments reveal the same divine truth. Tertullian sought to defend orthodox Christian belief against the gnostic tendencies present in Marcion's teachings, reinforcing the idea of continuity between the two Testaments rather than an outright rejection of one in favor of the other.

In contrast, Polycarp, Clement of Alexandria, and Justin Martyr did engage in theological discussions and defenses of the Christian faith, but Tertullian is particularly noted for his direct opposition to Marcionism through his writings, which helped shape the early Church's understanding of Scripture and doctrine.