John James Rambo is a fictional character in the Rambo franchise. He first appeared in the 1972 novel First Blood by David Morrell, but later became more famous as the protagonist of the film series, in which he was played by Sylvester Stallone. The portrayal of the character earned Stallone widespread acclaim and recognition. The character was nominated for American Film Institute's list 100 Years…100 Heroes and Villains. Following the success of the first movie, the term "Rambo" was occasionally used in media circles to describe a lone wolf who is reckless, uses violence to solve all problems, enters dangerous situations alone, and is exceptionally tough, callous, raw and aggressive.

David Morrell says that in choosing the name Rambo, he was inspired by "the sound of force" in the name of Rambo apples, which he encountered in Pennsylvania. These apples, in turn, were named for Peter Gunnarsson Rambo, who sailed from Sweden to America in the 1640s, and soon the name would flourish in New Sweden. The name Rambo was likely derived from a shortened form of Ramberget (a hill on the Hisingen island in Gothenburg, where Peter Gunnarsson was born) plus "bo" (meaning "resident of"). Today, many of his descendants can still be found in this region of the US. Morrell also felt that its pronunciation was similar to the surname of Arthur Rimbaud, the title of whose most famous work, A Season in Hell, seemed to him "an apt metaphor for the prisoner-of-war experiences that I imagined Rambo suffering". Furthermore, an Arthur J. Rambo was an actual U.S. soldier in Vietnam, but he never returned. His name can be seen on the Vietnam War Memorial wall in Washington, D.C.. He was granted the first name "John" as a reference to the Civil War era song "When Johnny Comes Marching Home Again".

In the novel and first film, Rambo appears as a soldier who suffers from post-traumatic stress disorder and has difficulty adjusting to normal life. He is shown to be prone to violence because of the torture he suffered at the hands of North Vietnamese soldiers in the Vietnam War. In the next films and novelizations, he is displayed as a man who wants to stay away from conflict but is willing to do anything to save his friends and the people he cares about from any danger. Due to his violent nature, many civil people tend to fear him. However, Colonel Samuel Trautman (who was his commanding officer in Vietnam and is probably his only friend) understands him and the pain and torture he has endured in the war and is the only one able to reason with him when he becomes an outlaw after incapacitating police officers in the town of Hope.

Rambo has a muscular physique due to his time as a soldier in the army and his intense training regimen. He has a high amount of strength and stamina. Rambo is an expert in surviving in dense forests against a large number of enemies due to his experiences in the Vietnam War. He is also an expert in guerrilla tactics, weapons, and hand-to-hand combat. Rambo has black hair and brown eyes. His height is 5 ft 10 in (1.78 m). In the DVD commentary for First Blood, Morell remarks that the inspiration for Rambo was World War II hero Audie Murphy.

In all five films, Rambo is portrayed by Sylvester Stallone. In the animated TV series, the character is voiced by Neil Ross.

According to Rambo: Last Blood, the character's full name is John Rambo and he was born on July 6, 1947, in Bowie, Arizona, to father Reevis Rambo (1920–2000) and mother Helga Rambo (1924–1969), as shown on the graves at Rambo's farm in Rambo: Last Blood. In Rambo: First Blood Part II, he is said to be of Native American and German descent; the character Major Marshall Roger T. Murdock says: "Of Indian and German descent. That's a hell of a combination!" The film's novelization reveals he has an Italian father and a Navajo mother. John's niece, Shirlene, is also well known. Rambo enlisted in the U.S. Army at the age of 17, on August 6, 1964, although he states in Rambo that he was "drafted into Vietnam". After he graduated from Rangeford High School in 1965, his military service began in January 1966. Rambo was deployed to South Vietnam in September 1966. He returned to the U.S. in 1967 and began training with the U.S. Army Special Forces at Fort Bragg, North Carolina, under Colonel Samuel Trautman's tutelage.

In late 1969, Rambo was redeployed to Vietnam as a member of a SOG brigade. He became part of a Special Forces long-range reconnaissance patrol unit, commanded by Colonel Trautman. Trautman's team received the code name of Baker Team and usually consisted of eight men. Other known members were Delmar Barry (a black operative who quickly became Rambo's best friend), Joseph "Joey" Danforth (another friend of Rambo), Manuel "Loco" Ortega, Paul Messner, Delbert Krackhauer, Giuseppe "Greasy Cunt" Colletta, and Ralph Jorgenson. In an event that would haunt Rambo for the rest of his life, Danforth died in Rambo's arms, after being fatally wounded by a rigged shoeshine box while their unit was on rest and recuperation time.

During a mission in November 1971, Rambo's unit came under surprise attack by NVA forces. Delmar, Rambo, and some other surviving members were captured by North Vietnamese forces near the Chinese-Vietnamese border and held at a POW camp, where many other American POWs were imprisoned and repeatedly tortured. Rambo's unit was decimated during the ordeal, but Delmar and Rambo managed to escape captivity in May 1972, and Rambo was immediately redeployed at his own request. At some point in his military career, he also received training in flying helicopters. Rambo finally received his official military discharge on September 27, 1974.