Robert John Downey Jr. (born April 4, 1965) is an American actor. Known for his charismatic performances and versatility, he was the highest-paid actor in Hollywood annually from 2013 to 2015. Downey's films as a leading actor have grossed over $14.3 billion worldwide, making him one of the highest-grossing film stars of all time.

At the age of five, Downey made his acting debut in his father Robert Downey Sr.'s film Pound (1970). He rose to prominence by working with the Brat Pack for the teen films Weird Science (1985) and Less than Zero (1987). His portrayal of Charlie Chaplin in the biopic Chaplin (1992) earned him the BAFTA Award for Best Actor and an Academy Award nomination. After serving time at the Corcoran Substance Abuse Treatment Facility on drug charges, Downey joined the television series Ally McBeal in 2000, earning a Golden Globe for his performance. In 2001, he was dismissed from the show following further drug-related arrests. He entered a court-ordered rehabilitation program and has remained sober since 2003.

After Mel Gibson paid his insurance bond, Downey made his film comeback with The Singing Detective (2003). He portrayed the titular character in Sherlock Holmes (2009)—which earned him a Golden Globe—and its sequel, subtitled A Game of Shadows (2011). Downey gained global recognition for starring as Iron Man in ten Marvel Cinematic Universe films, from Iron Man (2008) to Avengers: Endgame (2019). For his acclaimed portrayal of Lewis Strauss in Christopher Nolan's Oppenheimer (2023), he won an Academy Award, a Golden Globe, and a BAFTA Award for Best Supporting Actor. In 2024, he was nominated for a Primetime Emmy Award for the miniseries The Sympathizer and made his Broadway debut in the title role of Ayad Akhtar's McNeal.

In a career spanning more than five decades, Downey has won numerous accolades, including an Academy Award, a Daytime Emmy Award, three Golden Globe Awards, two BAFTA Awards, and three Screen Actors Guild Awards. Time named him one of the 100 most influential people in 2008, and Forbes featured him on the Celebrity 100 in 2013 and 2014. Downey has pursued music, releasing the jazz-pop album The Futurist (2004), which charted on the US Billboard 200. Divorced from Deborah Falconer, he has been married to Susan Levin since 2005, with whom he co-founded the production company Team Downey. He has three children: one with Falconer and two with Levin.

Robert John Downey Jr. was born in Manhattan, New York City, on April 4, 1965. His father, Robert Downey Sr. (né Elias), was a filmmaker, while his mother, Elsie Ann (née Ford), was an actress who appeared in Downey Sr.'s films. His father was one-half Lithuanian Jewish, one-quarter Hungarian Jewish, and one-quarter Irish, while his mother had Scottish, German, and Swiss ancestry. Downey's sister, Allyson, is two years older than him.

Due to his father's film projects, Downey moved frequently during his childhood, living in places such as Woodstock, New York, London, New Mexico, California, Connecticut, and Greenwich Village. From a young age, Downey was exposed to drugs: his father struggled with addiction, and his mother battled alcoholism. He has said that his father introduced him to marijuana at age eight, for which he later expressed regret. Downey mentioned that using drugs with his father created an emotional connection between them, explaining that, "When my dad and I used drugs together, it was his way of showing love for me in the only manner he knew." During his childhood, Downey appeared in small roles in his father's films. He made his acting debut at the age of five, portraying a sick puppy in the absurdist comedy Pound (1970), and at seven, he appeared in the surrealist Western Greaser's Palace (1972). Aged eleven and twelve, he attended Stagedoor Manor, a summer acting camp in upstate New York.

Downey was described as a hyperactive child who "tried to be cool", often teased by the older boys but popular with the girls. His parents divorced in 1977 when he was twelve; afterward, he lived with his mother in a fifth-floor apartment in New York, while his sister stayed with their father, who later took her to a boarding school. He attended Lincoln Junior High School for eighth grade and then Santa Monica High School for ninth and tenth grades, but dropped out in 1982. At age 17, he relocated to New York City to pursue acting full-time, working various jobs such as clearing tables at a Central Falls restaurant, working in a shoe store, and performing as "living art" at the nightclub Area to support himself during auditions. During this period, he also appeared in local theater and off-Broadway productions.

Downey made his stage debut in 1983 with a three-week run in Alms for the Middle Class at the Geva Theatre Center. He then appeared in the short-lived off-Broadway musical American Passion at the Joyce Theater, produced by Norman Lear. Downey's first credited film role was in Baby It's You (1983), though most of his scenes were cut. In his early film roles, he frequently portrayed misfit characters, and his portrayals of punk-like figures in several 1980s coming-of-age films led to his occasional association with the Brat Pack. In the drama film Firstborn (1984), he played a supporting role as the teenage friend of the protagonist. Downey then traveled to Los Angeles to film James Spader's Tuff Turf (1985), in which he played Spader's sidekick and a punk drummer. Later that year, his role as a bully in John Hughes's Weird Science (1985) marked his breakthrough. Downey starred as a more likeable radical socialist in the Alan Metter comedy film Back to School (1987).