Asuka Ryou's true identity. Hermaphrodite.
He and his army of demons hibernated for two million years after a battle against God, only to find out that human beings had taken over Earth in the meantime. To infiltrate their society and understand them more, Satan got his memories replaced with the ones belonging to a recently deceased human - a young man named Asuka Ryou. During his human life as Ryou, Satan met Fudou Akira and became his best friend, later encouraging him to become a devilman to protect humanity from demons.

Only after demons officially declared war against humans, he got his memory back. Despite having developed romantic feelings for Akira, Satan led his army until the end, wiping out humanity.