- Peter Sellers as:
- Group Captain Lionel Mandrake, a British RAF exchange officer
- President Merkin Muffley, the President of the United States
- Dr. Strangelove, the wheelchair-bound nuclear war expert and former Nazi
- George C. Scott as General Buck Turgidson, a jingoist general
- Sterling Hayden as Brigadier General Jack D. Ripper, a paranoid ultra-nationalist
- Keenan Wynn as Colonel Bat Guano, the Army officer who finds Mandrake and the dead Ripper
- Slim Pickens as Major T. J. "King" Kong, the B-52 Stratofortress bomber's commander and pilot
- Peter Bull as Soviet Ambassador Alexei de Sadeski
- James Earl Jones as Lieutenant Lothar Zogg, the B-52's bombardier
- Tracy Reed as Miss Scott, General Turgidson's secretary and mistress, the film's only female character. Reed also appears as "Miss Foreign Affairs," the centerfold in the June 1962 issue of Playboy magazine that Major Kong is shown reading in the cockpit.
- Shane Rimmer as Capt. Ace Owens, the B-52 co-pilot
Peter Sellers's multiple roles
Columbia Pictures agreed to finance the film on condition that Peter Sellers play at least four major roles. This condition stemmed from the studio's opinion that much of the success of Kubrick's previous film Lolita (1962) was based on Sellers's performance, in which his single character assumes a number of identities. Sellers had also played three roles in The Mouse That Roared (1959). Kubrick accepted the demand, later explaining that "such crass and grotesque stipulations are the sine qua non of the motion-picture business."
Sellers ended up playing three of the four roles written for him. He had been expected to play Air Force Major T. J. "King" Kong, the B-52 Stratofortress aircraft commander, but from the beginning Sellers was reluctant. He felt his workload was too heavy and he worried he would not properly portray the character's Texas accent. Kubrick pleaded with him and asked screenwriter Terry Southern (who had been raised in Texas) to record a tape with Kong's lines spoken in the correct accent. Using Southern's tape, Sellers managed to get the accent right, and started shooting the scenes in the airplane, but then Sellers sprained an ankle and could not work in the cramped cockpit set.
Sellers is said to have improvised much of his dialogue, with Kubrick incorporating the ad-libs into the written screenplay so that the improvised lines became part of the canonical screenplay, a practice known as retroscripting.
- Group Captain Lionel Mandrake
According to film critic Alexander Walker, the author of biographies of both Sellers and Kubrick, the role of Group Captain Lionel Mandrake was the easiest of the three for Sellers to play, as he was aided by his experience of mimicking his superiors while serving in the RAF during World War II. There is also a heavy resemblance to Sellers's friend and occasional co-star Terry-Thomas and prosthetic-limbed RAF ace Douglas Bader.
- President Merkin Muffley
For his performance as President Merkin Muffley, Sellers flattened his natural English accent to resemble an American Midwesterner. Sellers drew inspiration for the role from Adlai Stevenson, a former Illinois governor who was the Democratic candidate for the 1952 and 1956 presidential elections and the U.N. ambassador during the Cuban Missile Crisis.
In early takes, Sellers faked cold symptoms to emphasize the character's apparent weakness. This caused frequent laughter among the film crew, ruining several takes. Kubrick ultimately found this comic portrayal inappropriate, feeling that Muffley should be a serious character. In later takes Sellers played the role straight, though the President's cold is still evident in several scenes.
In keeping with Kubrick's satirical character names, a "merkin" is a pubic hair wig. The president is bald, and his last name is "Muffley"; both are additional homages to a merkin.
- Dr. Strangelove
Dr. Strangelove is an ex-Nazi scientist, suggesting Operation Paperclip, the US effort to recruit top German technical talent at the end of World War II. He serves as President Muffley's scientific adviser in the War Room. When General Turgidson wonders aloud what kind of name "Strangelove" is, saying to Mr. Staines (Jack Creley) that it is not a "Kraut name," Staines responds that Strangelove's original German surname was "Merkwürdigliebe," without mentioning that "Merkwürdigliebe" translates to "Strangelove" in English. Twice in the film, Strangelove "accidentally" addresses the president as "Mein Führer". Dr. Strangelove did not appear in the book Red Alert.
The character is an amalgamation of RAND Corporation strategist Herman Kahn, mathematician and Manhattan Project principal John von Neumann, rocket scientist Wernher von Braun (a central figure in Nazi Germany's rocket development program recruited to the US after the war), and Edward Teller, the "father of the hydrogen bomb." There is a common misconception that the character was based on Henry Kissinger, but Kubrick and Sellers denied this; Sellers said, "Strangelove was never modeled after Kissinger—that's a popular misconception. It was always Wernher Von Braun."
The wheelchair-bound Strangelove furthers a Kubrick trope of the menacing, seated antagonist, first depicted in Lolita through the character "Dr. Zaempf." Strangelove's accent was influenced by that of Austrian-American photographer Weegee, who worked for Kubrick as a special photographic effects consultant. Strangelove's appearance echoes the mad scientist archetype as seen in the character Rotwang in Fritz Lang's film Metropolis (1927). Sellers's Strangelove takes from Rotwang the single black gloved hand (which in Rotwang's case is mechanical because of a lab accident), the wild hair and, most importantly, his inability to be completely controlled by political power. According to film critic Alexander Walker, Sellers improvised Dr. Strangelove's lapse into the Nazi salute, borrowing one of Kubrick's black leather gloves for the uncontrollable hand that makes the gesture. Dr. Strangelove apparently suffers from diagnostic apraxia (alien hand syndrome). Kubrick wore the gloves on the set to avoid being burned when handling hot lights, and Sellers, recognizing the potential connection to Lang's work, found them to be menacing.
Slim Pickens as Major T. J. "King" Kong
Slim Pickens, an established character actor and veteran of many Western films, was eventually chosen to replace Sellers as Major Kong after Sellers's injury. Terry Southern's biographer, Lee Hill, said the part was originally written with John Wayne in mind, and that Wayne was offered the role after Sellers was injured but he immediately turned it down. Dan Blocker of the Bonanza western television series was approached to play the part, but according to Southern, Blocker's agent rejected the script as being "too pinko." Kubrick then recruited Pickens, whom he knew from Pickens's work in Marlon Brando's One-Eyed Jacks.
Fellow actor James Earl Jones recalls, "He was Major Kong on and off the set—he didn't change a thing—his temperament, his language, his behavior." Pickens was not told that the movie was a comedy and was only given the script for scenes he was in, to get him to play it "straight."
Kubrick biographer John Baxter explains, in the documentary Inside the Making of Dr. Strangelove:
As it turns out, Slim Pickens had never left the United States. He had to hurry and get his first passport. He arrived on the set, and somebody said, "Gosh, he's arrived in costume!," not realizing that that's how he always dressed ... with the cowboy hat and the fringed jacket and the cowboy boots—and that he wasn't putting on the character—that's the way he talked.
Pickens, who had previously played only minor supporting and character roles, said his appearance as Maj. Kong greatly improved his career. He later commented, "After Dr. Strangelove the roles, the dressing rooms and the checks all started getting bigger."
George C. Scott as General Buck Turgidson
Kubrick tricked Scott into playing the role of Gen. Turgidson far more ridiculously than Scott was comfortable doing. Kubrick talked Scott into doing over the top "practice" takes, which Kubrick told Scott would never be used, as a way to warm up for the "real" takes. Kubrick used these takes in the final film, causing Scott to swear never to work with Kubrick again.
During the filming, Kubrick and Scott had different opinions regarding certain scenes, but Kubrick got Scott to conform largely by repeatedly beating him at chess, which they played frequently on the set. Scott, a skilled player himself, later said that while he and Kubrick may not have always seen eye to eye, he respected Kubrick immensely for his skill at chess.