A ronin was a samurai with no lord or master during the feudal period (1185–1868) of Japan. A samurai became masterless from the ruin or fall of his master (as in the case of death in a war), or after the loss of his master's favor or privilege.

The word rōnin literally means "drifting person". The term originated in the Nara and Heian periods, when it referred to a serf who had fled or deserted his master's land. It then came to be used for a samurai who had lost his master.

Thousands of modern works of Japanese fiction set in the Edo period cast characters who are ronin. They are often portrayed as yojimbo (bodyguards) or as mercenary fighters. Another stereotypical occupation for fictional ronin is the umbrella-maker.

Bound and dedicated men, most samurai resented the personal freedom that the wandering ronin enjoyed. Ronin were the epitome of self-determination; they were independent men who dictated their own path in life, answering only to themselves and making decisions as they saw fit.