Mario Lopez (born October 10, 1973) is an American actor and television host. He has appeared on several television series, in films, and on Broadway. He is known for his portrayal of A.C. Slater on Saved by the Bell, Saved by the Bell: The College Years, and the 2020 sequel series. He has appeared in numerous projects since, including the third season of Dancing with the Stars and as host for the syndicated entertainment news magazine shows Extra and Access Hollywood. He has also hosted America's Best Dance Crew for MTV. In 2012, he co-hosted the second season of the American version of The X Factor with Khloé Kardashian, and was the sole host for the third and final season.

Lopez was born on October 10, 1973, in Chula Vista, California, the son of Elvira Soledad Trasviña and Mario Alberto López Pérez. Lopez was raised in a Catholic family. His parents are both emigrants from Mexico. His father was born in Culiacán, Sinaloa, and his mother in Tijuana, Baja California. His younger sister, Marissa, is married to former NFL Minnesota Vikings and Houston Texans linebacker Kailee Wong.

Lopez started dance education at age three, training in tap and jazz. He also did tumbling, karate and wrestling at his local Boys and Girls Club when he was 7 years old. He excelled at these as well as other activities in which his mother enrolled him. During high school at Chula Vista High School, he was on the school's wrestling team at the weight class of 160 lb (73 kg). He placed 2nd in the San Diego Section competition and 7th in California his senior year. He graduated in 1991.

Lopez was discovered by a talent agent at a dance recital when he was 10 years old. He initially worked in local advertisements and commercials before making TV appearances.

Lopez began acting in 1984 when he appeared as younger brother Tomás in the short-lived ABC comedy series a.k.a. Pablo. That same year, he was cast as a drummer and dancer on Kids Incorporated; he performed on three seasons. In March 1987, he was cast as a guest star on the sitcom The Golden Girls as a Latino boy named Mario who faces deportation. He was cast in a small part in the film Colors (1988) as Felipe's friend.

Lopez was cast in 1989 as A.C. Slater in the television Saturday-morning series sitcom Saved by the Bell (1989–1993), and its spinoff Saved by the Bell: The College Years (1993–1994). On February 4, 2015, Lopez reunited with Mark-Paul Gosselaar, Elizabeth Berkley, Dennis Haskins, and Tiffani Thiessen on The Tonight Show Starring Jimmy Fallon, where they appeared in a Saved by the Bell sketch with Fallon. In 2020, Lopez reprised the role of A.C. Slater in Peacock's sequel series, Saved by the Bell.

In 1997, Lopez starred as Olympic diver Greg Louganis in the television film Breaking the Surface: The Greg Louganis Story. The following year, he was cast as Bobby Cruz in the USA Network series Pacific Blue for two seasons before it was canceled after the fifth season; he then went on to guest star on Resurrection Blvd., Eve, and The Bad Girl's Guide. In March 2006, Lopez joined the cast of the daytime soap opera The Bold and the Beautiful playing the role of Dr. Christian Ramirez. On July 18, 2006, he was released from his B&B contract. Later that year, Mario guest-starred as a plastic surgeon who drives Christian Troy to jealousy when he sees him naked in the shower in an episode of FX Network's Nip/Tuck during the show's fourth season, which began in autumn 2006. He also made an appearance on George Lopez as a police officer in late 2006.

Also in the fall of 2006, Lopez signed on as a contestant on the third season of Dancing with the Stars on ABC with professional partner and then-girlfriend Karina Smirnoff who was making her series debut. They finished in second place, losing to the team of Emmitt Smith and Cheryl Burke.