A samurai (Japanese: 大名) is a traditional Japanese soldier who serves under a daimyō, or feudal lord, usually in return for land, similar to ninja (though not nearly as widespread). It is not just a name, but a person's title. Several characters in the TMNT multiverse have been known primarily, notably or only as "Samurai".
During the Japanese history, the samurai were eventually organized into one of the four classes of Japan, following the conclusion of the Sengoku jidai and the establishment of the Tokugawa shogunate. They were the only class allowed to possess weapons and wear them in public. They also maintained the right to execute commoners who disrespected them.
They were disbanded as a class in 1873 by Emperor Meiji and replaced with a modern military force. However, the military class which took their place continued to dominate the Japanese political system until the end of World War II and samurai ethics continue to influence Japanese society today and part of the Japanese nobility.