Marcelo Andres Ríos Mayorga (born 26 December 1975) is a former world No. 1 tennis player from Chile. Nicknamed El Chino ("The Chinese") and El zurdo de Vitacura ("The Lefty from Vitacura"), he became the first Latin American player to reach the top position on the Association of Tennis Professionals (ATP) singles rankings in 1998. He held the world No. 1 ranking for six weeks. He also held the top ranking in both juniors and seniors. He was the first player to win all three clay-court Masters Series tournaments (Monte Carlo, Rome, and Hamburg) since the format began in 1990. Despite winning five Masters titles overall, he is the only male player in the open era to have been world No. 1 while never managing to win a Grand Slam singles tournament in his career. He did reach the 1998 Australian Open final, losing to Petr Korda in straight sets. Until Rafael Nadal in 2008, Ríos was the last left-handed player to become world No. 1.
He retired prematurely in July 2004, after being overtaken by a back injury. He played his last ATP Tour level tournament while only 27 years old at the 2003 French Open.