Ra's al Ghul may have founded the League of Assassins, but he would leave much of its affairs in the hands of Professor Ebeneezer Darrk and his second in command: the Sensei, an aged martial arts master from Hong Kong. After earning Ra's enmity (for reasons unknown) Daark died during a plot to kidnap Talia al Ghul which was foiled by The Batman.
The Sensei Han-son was put in charge of the League afterwards, however he would prove just as disloyal as his predecessor, and the Sensei would eventually struggle with Ra's al Ghul for the control of the organization. For a time, the Sensei was possessed by the spirit called Jonah, who in Sensei's body was responsible for the murder of Boston Brand, who became Deadman after his death. After a struggle with Deadman and Rama Kushna, Jonah was destroyed and the Sensei resumed control of his body. For a brief time, the Sensei assumed leadership of the League of Assassins.
By this stage, the Sensei was clearly insane (if he had not been before) with no goals other than to raise assassination to an artform. Among other crimes he used Bronze Tiger, the brainwashed partner of Richard Dragon, to carry out a number of assassinations. Most notably he used the Bronze Tiger to occupy Batman in battle, while other assassins killed Batman's friend Kathy Kane.
He next attempted to kill a number of dignitiaries by having the League plant explosives along a fault line, stating that using a force of nature to carry out an assassination would be his greatest work of art. Although Batman arrived in time to rescue the delegates, he was unable to stop the earthquake. With no time to pursue the Sensei himself, Batman was forced to allow Ra's al Ghul to go after the assassin. Sensei then engaged himself in a fight to the death with Ra's al Ghul, during which both of them were swallowed by the earthquake. Ra's lived thanks to his rejuvenating Lazarus Pit. The Sensei also somehow survived, to reappear in the "Batman: The Resurrection of Ra's al Ghul" storyline, wherein he is revealed to be al Ghul's father. When Ra's and Batman seek the Fountain of Youth in the Valley of Nanda Parbat, Sensei confronts them both, stabbing Ra's's decaying body and then attacking Batman, arrogantly informing the Dark Knight that, while he can only maintain the necessary physical strength to vanquish Batman for two minutes at his age, he only needs one minute to break him. However, Batman is able to take him by surprise, hurling both of them into the Fountain; it destroys Sensei due to his impure spirit, but Batman is not only healed, but apparently slightly rejuvenated by his dip in the waters.
In Other Media
- The Sensei appeared in the comic book Batman Gotham Adventures (based on Batman: The Animated Series). Unlike his counterpart in the mainstream DC Universe, this version of the Sensei was directly responsible for the murder of Boston Brand, creating the ghostly hero Deadman. In the comics, the Sensei had an operative named the Hook kill Boston Brand.
- The Sensei served the Ra's al Ghul of the animated series, training assassins for the immortal's use. After being tracked down to the League's headquarters in Tibet, the Sensei engaged both Batman and Batgirl in combat, and was apparently defeating them when the battle was broken up by Ra's and Talia. Ra's required Batman for his plans, and when Batman refused to leave without the Sensei, Ra's ordered him to go with Batman. Neither wishing to get in the way of Ra's plans nor to spend the rest of his days in prison, the old man chose a third option and quietly walked out one of the windows of his mountain hideaway, falling to his death.
- In Batman Begins, an old man that lives nearby the headquarters of the League of Shadows resembles to the look of the Sensei. After Bruce saved Ducard's life and takes it to this old man, he says that he will tell Ducard that Bruce saved him.
- In Young Justice, he appears as a high-ranking member of the League of Shadows. He had abducted Dr. Serling Roquette in order to have her create the "Fog." After Red Arrow had rescued Serling Roquette, Sensei sends Cheshire, Hook, and Black Spider to Happy Harbor in order to assassinate Serling Roquette when she creates the "Anti-Fog." When Black Spider and Hook get captured and Cheshire escapes, it is shown that Sensei is in league with Project Cadmus' Board of Directors and tells them that they have someone on the inside to help them.
- In Gotham, Sensei (also known as The Temple Shaman) is the true leader of the Court of Owls, and also works for Ra's al Ghul and the League of Assassins. He has Bruce Wayne abducted and begins to train him to unlock the hidden potential in his mind, and manages to brainwash Bruce to be a loyal servant of his in preparation for meeting Ra's. Once the Court of Owls have finished weaponizing a virus to destroy Gotham City, Sensei has all ruling members of the Court killed, which is also in retaliation for them having Bruce's parents Thomas and Martha killed, something of which Sensei opposed of as he respected them. At Wayne Enterprises, Sensei attempts to cohere Bruce into fulfilling his destiny and detonating the virus, but they are interrupted by Alfred Pennyworth. Sensei detonates the bomb himself and ends up being shot, and before he dies of his wounds he urges Bruce to find the "Demon's Head".