A rikishi (力士), sumōtori (相撲取り) or, more colloquially, osumōsan (お相撲さん), is a sumo wrestler. Although used to define all wrestlers participating in sumo wrestling matches, the term is more commonly used to refer to professional wrestlers, employed by the Japan Sumo Association, who participate in professional sumo tournaments in Japan, the only country where sumo is practiced professionally.

Sumo is a form of competitive full-contact wrestling where a rikishi (wrestler) attempts to force his opponent out of a circular ring (dohyō) or into touching the ground with any body part other than the soles of his feet.