Who is meant by “the one who conquers”?

The term echoes the refrain found at the end of each of the seven letters of Revelation 2 and 3 to refer to those who are faithful to the word of Christ (Revelation 2:7, Revelation 2:11, Revelation 2:17, Revelation 2:26–27; Revelation 3:5, Revelation 3:12, Revelation 3:21). In those letters the challenge was placed before the readers of the seven churches to persevere in the real-life context in which they found themselves, with the promise that those who conquered would receive an eternal reward. In the intervening chapters John has shown his readers who they are up against, that is, whose temptations they need to conquer. Cruel and evil though these temptations may be (Revelation 13:7, Revelation 13:16–17), the good news is that Satan is defeated (Revelation 12:7–9; Revelation 20:2, Revelation 20:10) and so are his lackeys (Revelation 19:20; Revelation 20:11–13). So the redeemed may be confident that in Jesus Christ victory is theirs, and so they should assertively lean into the battle.