Read this: The use of the word "heresy" was given wide currency by Irenaeus in his 2nd century tract Contra Haereses (Against Heresies) to describe and discredit his opponents during the early centuries of the Christian community.[citation needed] He described the community's beliefs and doctrines as orthodox (from ὀρθός, orthos "straight" + δόξα, doxa "belief") and the Gnostics' teachings as heretical.[citation needed] He also pointed out the concept of apostolic succession to support his arguments.

Who wrote about their opponents in the 200's
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable