Desi Arnaz, Jr. (born January 19, 1953) is an American actor and musician.

He was born Desiderio Alberto Arnaz, IV at Cedars of Lebanon Hospital in Hollywood, California, the son of famous acting team Desi Arnaz and Lucille Ball. His older sister is actress Lucie Arnaz.

His birth was one of the most publicised and anticipated births in TV history. His parents were appearing in the sitcom I Love Lucy and Ball's pregnancy was written into the storyline of the show, a move considered daring and groundbreaking in those conservative times. When Lucille Ball went to the hospital and gave birth to Desi, Jr., the network ran the episode where the fictional Lucy Ricardo gave birth to Little Ricky and millions of TV viewers watched.

By age twelve, Arnaz, Jr., was working as a drummer with the group Dino, Desi, & Billy. The other members were Dino Martin (son of Dean Martin) and Billy Hinsche. The group scored two hit singles during 1965.

In 1968, he and his sister, Lucie, played opposite their mother in her series Here's Lucy, as her children. Arnaz, Jr.'s acting career extended into the 1980s with appearances in numerous made for TV productions and guest roles on various series, including the short lived Automan.

He returned to acting to play his father in the movie Mambo Kings (1992).

Arnaz, Jr., has been married and divorced from actress Linda Purl.

He was romantically linked to Patty Duke, Liza Minnelli and Victoria Principal. When Patty Duke gave birth to Sean Astin many assumed that Arnaz, Jr., was the biological father. Years later, Arnaz, Jr., took a blood test to determine Sean Astin's paternity. The test proved that Arnaz was not the father.