Steven Frederic Seagal (/sɪˈɡɑːl/ sih-GAHL; born April 10, 1952) is an American actor, producer, screenwriter, martial artist, and musician. A 7th-dan black belt and shihan in Aikikai aikido, he began his adult life as a martial arts instructor in Japan, where he became the first non-Japanese and American to operate an aikido dojo. He later moved to Los Angeles, where he continued teaching aikido. In 1988, Seagal made his acting debut in Above the Law, which is regarded as the first American film to feature aikido in fight sequences.

By 1991, he had starred in three commercially successful films, and went on to achieve greater fame in Under Siege (1992), where he played Navy SEAL counter-terrorist expert Casey Ryback, a role he reprised in the sequel Under Siege 2: Dark Territory (1995). In 1994, he starred in his directorial debut film On Deadly Ground. During the latter half of the 1990s, Seagal starred in three more feature films and the direct-to-video film The Patriot. Subsequently, his career shifted to mostly direct-to-video productions. He has since appeared in films and reality shows, most notably as the main villain in Robert Rodriguez's Machete (2010), and Steven Seagal: Lawman, which depicted Seagal performing duties as a reserve deputy sheriff.

Seagal is a guitarist and has released two studio albums, Songs from the Crystal Cave and Mojo Priest, and performed on the scores of several of his films. He has worked with Stevie Wonder and Tony Rebel, who both performed on his debut album. He has been involved in a line of "therapeutic oil" products and energy drinks. Seagal is an environmentalist, animal rights activist, and supporter of 14th Dalai Lama Tenzin Gyatso. In 2004, he was inducted into the Martial Arts History Museum Hall of Fame.

Seagal has been the subject of controversy during his career. Since 1991, multiple women have accused Seagal of sexual harassment or assault. A supporter of Vladimir Putin, he backed the Russian annexation of Crimea in 2014 and the Russian invasion of Ukraine in 2022. He was granted both Russian and Serbian citizenship in 2016. In 2018, he was appointed Russia's special envoy to the U.S.

Steven Seagal was born on April 10, 1952, in Lansing, Michigan, the son of Patricia Anne Fisher, a medical technician, and Samuel Seagal, a mathematics teacher. His mother was of Irish descent, while his father was Jewish. His paternal grandparents were Russian Jewish immigrants. During an interview for the Russian talk show Let Them Talk, Seagal stated that he has paternal ancestors from the Siberian city of Vladivostok, as well as Belarus and Saint Petersburg. He claims that genetic testing determined that he has Yakut and Buryat ancestry as well. When he was 5, Seagal moved with his parents to Fullerton, California. His mother later told People magazine that prior to the move Seagal was frail and suffered from asthma: "He was a puny kid back then. But he really thrived after the move [to California]."

Seagal attended Buena Park High School in Buena Park, California, and Fullerton College between 1970 and 1971. Seagal has been described as a “pathological liar” due to his propensity of making greatly exaggerated or outright fabricated statements about his personal life and achievements. For instance, Seagal has stated that he was a student of the founder of aikido, Morihei Ueshiba, despite the fact that Ueshiba died in 1969 when Seagal was 17 and five years before Seagal moved to Japan at age 22 — when he moved there to avoid the draft for the Vietnam War by marrying a Japanese national.

According to Seagal's first wife, Miyako Fujitani: "I met Steven in California in the fall of 1974. He followed me back to Japan in October. We got married in December 1974." Fujitani was a second-degree black belt and daughter of an Jūsō, Osaka aikido master who had come to Los Angeles to teach aikido. After they married, they had a son, Kentaro, and a daughter, Ayako. Seagal taught at the school owned by Miyako's family and earned his aikido black belt in 1978. While there, he ran the Fujitani family dojo on behalf of Miyako's retired father, making him the first westerner to operate an Aikido dojo. Interviewed in 1993, Fujitani stated that: "The only reason Steven was awarded the black belt was because the judge, who was famous for his laziness, fell asleep during Steven's presentation. The judge just gave him the black belt."

Seagal has claimed that he helped train CIA agents in Japan: "They saw my abilities, both with martial arts and with the language. You could say that I became an advisor to several CIA agents in the field, and through my friends in the CIA, I met many powerful people and did special works and favors." Fujitani has refuted these allegations and has also dismissed Seagal's claims that he had combatted yakuza. There is no evidence that Seagal has ever worked with the Central Intelligence Agency. In the early-1980s, Seagal had aspirations to return to America and become a movie star. Fujitani then "scrimped and saved for years, even denying herself and her children necessities, to help pay his way home." According to Fujitani, "he then availed himself of her savings and hied off."