The Sensei was the immortal father of Ra's al Ghul.
After his son found the key to immortality and broke the key to mortality, the Sensei helped him lead the League of Assassins for what seemed to be forever. However, upon the arrival of the 21st Century, the Sensei betrayed his son, seeing him as weak after the Batman took care of Dr. Darrk for him. Attempted to supplant al Ghul, the Sensei even tried to kidnap his granddaughter. However, the Sensei was defeated.