In feudal Japan, a rōnin was a type of samurai who had no lord or master and in some cases, had also severed all links with his family or clan. A samurai becomes a rōnin upon the death of his master, or after the loss of his masters favor. Rōnin were known to operate or serve as hired muscle for gangs that ran gambling rings, brothels, protection rackets, and similar activities. Many were petty thieves and muggers. The criminal segment gave the rōnin of the Edo period a persistent reputation of disgrace, with an image of thugs, bullies, cutthroats, and wandering vagrants. Not having the status or power of employed samurai, rōnin were often disreputable and festive, the group targeted humiliation or satire. It was undesirable to be a rōnin, as it meant being without a stipend or land. As an indication of the shame felt by samurai who became rōnin, Lord Redesdale recorded that a rōnin killed himself at the graves of the forty-seven rōnin.

In modern times, the term "ronin" has become nearly as popular as other famous Japanese terms such as samurai or ninja. The term is used in various media, including manga, anime, superheroes, and Hollywood films.