Who was the first actor to play the Joker on the Batman television series?

Context: César Julio Romero Jr. was an American actor and activist. He was active in film, radio, and television for almost sixty years.

His wide range of screen roles included Latin lovers, historical figures in costume dramas, characters in light domestic comedies, and the Joker on the Batman television series, which was included in TV Guide's 2013 list of The 60 Nastiest Villains of All Time. He was the first actor to play the character.

Answer: César Julio Romero Jr. played was the first actor to play the Joker.