The Ring of Five are the main antagonists of the original Shinobi arcade game and the leaders of the original Zeed Crime Syndicate. Under the leadership of the Masked Ninja, they sought to bring about a new feudal era by starting a civil war, by using the kidnapped Oboro Ninja Clan children, and have them brainwashed and trained to be their loyal and elite assassins but were defeated by Joe Musashi, the star ninja of the clan.
- Ken-Oh: A muscular ninja who was a master of Katonjutsu (火遁術 Fire-style Ninjutsu). His skills were enough to gain the attention of the Masked Ninja. With his power he began helping in the kidnappings of the Oboro Village's children, but his life was ended by the super ninja Joe Musashi.
- Black Turtle: A weapon smuggler who has sold arms to many a crime group and terrorist, his resources caught Zeed's attention, and under the guidance of the Masked Ninja, he became one of the Ring of Five. Despite being able to carry loads of men it was for naught as he perished at the blade of Joe Musashi.
- Mandara: A victim of the Masked Ninja's schemes, Mandara was once a peace loving guru who possessed incredible psychic powers. Zeed desired his power, but he refused them. Not taking no for an answer, Zeed had him captured and tortured him trying to get him to cooperate. When he refused again, the killed him and took his brain, and grafted it in a super-computer that they created, which forced his brain to pump immense psychic energy to attack Joe Musashi. Only by destroying the Mandara Master computer, was the guru able to find peace.
- Lobster: a ninja dressed in crimson samurai armor. Originally an honorable fighter, his desire for glory corrupted him and he became ambitious without reason. Seeing his incredible fighting skills and swordsmanship, the Masked Ninja appeared and gave him a place at his side as a member of the Ring of Five. After the children of the Oboro were rescued from an abandoned temple he had set up base in, he challenged Joe Musashi and was all but impervious to his attacks. When Joe realized his helmet was his weakness, he hurled shuriken at it and damaged it to the point that Lobster's soul was forced out.
- The Masked Ninja:The mastermind of Zeed, the Masked Ninja is an enigma to all, concealed behind a Hannya Mask. Do to his mastery of martial arts, Ninjutsu and dark magic, he ruled Zeed with an iron fist and tolerated failure from no one. Rumors speculated that he belonged to the same clan as Joe Musashi once, and was at one time a close person to him. This proved to be true when it was discovered that he was Nakahara, Joe's instructor in the Oboro School's Ninjutsu. Ambitious and frustrated beyond reason, he became obsessed with the mad idea to recreate the Sengoku period. When Joe realized what he had become, Musashi was left with no choice but to cut him down.
- The name is an allusion to Miyamoto Musashi's Book of Five Rings; a famous manuscript on swordsmanship and martial philosophy.