A diadem is a crown, a symbol of royal power and authority. The great red dragon of Revelation 12:3 sported “seven diadems” on his “seven heads” to convey his sense of (would be) kingship. His first sidekick, the beast from the sea, had “ten diadems on its [ten] horns” (Revelation 13:1) to demonstrate how much power this bully had. The rider on this horse has one “head” (nothing gross about him!) and on his head (not horns; he’s not a bully) are “many diadems.” When David defeated the Ammonites, the king’s crown was placed on David’s head (1 Chronicles 20:2). The rider of this horse had gone out conquering and to conquer (Revelation 6:2) and now appears with “many diadems” on his head, evidence of his numerous victories over every king who had sided with God’s enemies, Revelation 17:12–14). The term “many” certainly shows his superiority over the dragon (with one crown per head) and the beast (with ten).
12 His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself.