The Eternal Champion is a being with amazing powers. To aid him in his fight against The Overlord, he brought nine warriors back to life, only to pit them against each other, the winner aiding him in the fight. He would later relent on this after persuasion from Shadow Yamoto and Midknight (or this simply may have been his plan all along).
In the stories in which he features, The Eternal Champion is a typical teacher; keen to further his students' education but not afraid to appear strict and enact discipline, he remains in Fortress Eternity while his champions carry out his work. It is unknown why he didn't join the fight, particularly considering he has exemplary martial arts prowess.