Merlin is a popular wizard because of his legendary status in Arthurian myths and tales. He is known for his magical abilities, wisdom, and his role as a mentor to King Arthur. Merlin's character has been portrayed in various forms of media, from literature to films and television shows, which has helped to solidify his place in popular culture. Additionally, the mystery and intrigue surrounding Merlin's origins and powers have also contributed to his enduring popularity as a beloved wizard character.