The Mysterious Warrior (Japanese: 謎の格闘家 Romaji: Nazo no Kakutōka, literally the "mysterious martial artist) is the final boss in the Famicom/NES and PC Engine versions of Double Dragon II: The Revenge, replacing Willy Mackey as the main antagonist in those versions.
The Mysterious Warrior's true name and origin are unknown. All that it is known is that he is the successor of a deadly martial art known as Gensatsuken (幻殺拳), whose school has been in conflict with the Lee brothers' own style of Sōsetsuken (双截拳) for generations due to their contrasting ideals. He forms his own organization following the downfall of the Black Warriors, targeting various martial artists, including the students of the Lee brothers' own school. When Billy Lee's girlfriend, Marian, is killed during one of their attacks, the Lee brothers pursue the organization until reaching their island stronghold, eventually coming face to face with the leader himself. After being defeated by the Lee brothers, the Warrior tells the Lee brothers about the prophecy that has been passed down within his school. After his death, the Lee brothers return to their home only to find that Marian has been miraculously brought back to life.
- While his organization is never given a name in the Japanese version, the English localization refers to them as the "Shadow Warriors" in the opening sequence. The only other time the term "Shadow Warrior" appears in the English script is when Billy (or Jimmy) uses it to address the Mysterious Warrior himself prior to the final confrontation. The "Shadow Warriors" would be used as the name of the enemy organization in Super Double Dragon and Double Dragon Advance.
- The PC Engine version of Double Dragon II features an alternate ending on the easiest difficulty setting in which the Mysterious Warrior escapes after the first phase of the final battle, mocking the Lee brothers for their failure to defeat him.
- In Double Dragon Advance, a group of enemy characters modeled after the Mysterious Warrior appear as an elite enemy group that serve as Willy's bodyguards. They are known as the Five Emperors and are successors of a martial art known as Gensetsuken (幻截拳), appearing as the end bosses of the penultimate stage. When the player confronts Raymond, the head of the group, the standard boss theme is replaced by the Mysterious Warrior's theme from Double Dragon II.