Boss X is the main villain and final boss of Red's storyline in SaGa Frontier. Boss X is a strange creature on a huge robotic body, and the true leader of Black X. His past is a complete mystery. He is fought inside Black X's base, after Alkaiser defeats the Four Emperors sent by Dr. Klein. Annoyed by Klein's failure on defeating Alkaiser, Boss X shoves him away and decides to fight Alkaiser by himself, but he also ends defeated, and with his defeat Black X is ultimately finished as well.