Birdman is one of the Supermen, the guardians of the universe. He is the one who made Mitsuo, Booby, Sumire, and Hozen Oyama to permans and told them not to tell their secret identities to anyone.
Birdman was a hero on the super planet. He come to Earth and made Mitsuo, Booby, Sumire, and Hozen Oyama to permans. He told them not to tell anyone about this.
Meet the Grand Master
Birdman was walking on Earth when he first meet the Grand Master. The Grand Master made the wars to succeed his plans. Birdman and the permans stop this, destroy The Grand Master's plan.