Marcelo Andrés Ríos Mayorga (born December 26, 1975) is a former World No. 1 tennis player from Chile. Nicknamed El Chino ("Chinaman") and El zurdo de Vitacura ("Vitacura's Lefty"), 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 has held the top ranking in both juniors and seniors. He was the first player to win the three clay-court Masters Series tournaments (Monte Carlo, Rome, and Hamburg) since the format began in 1990. 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.

He retired prematurely in 2004, after being overtaken by a back injury. He played his last ATP level tournament while only 27 years old at the 2003 French Open.

Ríos began playing tennis at the age of 11 at the Sport Francés golf club in Vitacura (Greater Santiago), adjacent to his house.