The King and I is a stage musical, the fifth by the team of Richard Rodgers and Oscar Hammerstein II. The work is based on the 1944 novel Anna and the King of Siam by Margaret Landon and derives from the memoirs of Anna Leonowens, who became governess to the children of King Mongkut of Siam in the early 1860s. The story deals with the experiences of the British schoolteacher, who is hired as part of the King's drive to modernize his country. The relationship between the King and Anna is marked by conflict through much of the play, as well as by a love that neither is able to express. The musical premiered on March 29, 1951 at Broadway's St. James Theatre.

In 1950, theatrical attorney Fanny Holtzmann was looking for a part for her client, veteran leading lady Gertrude Lawrence. Holtzmann realized that Landon's book would be an ideal vehicle and contacted Rodgers and Hammerstein, who were initially reluctant, but who agreed to write the musical. The pair initially sought Rex Harrison to play the supporting part of the King?he had played the role in the 1946 movie made from Landon's book?but Harrison was unavailable. They settled on Russian-American actor Yul Brynner.

The musical was an immediate hit, winning Tony Awards for Best Musical, Best Actress (for Lawrence) and Best Featured Actor (for Brynner). Lawrence died unexpectedly of cancer a year and a half after the opening, and the role of Anna was played by other actresses during the remainder of the Broadway run of over three years (1,246 performances). A national tour and a hit London run followed, together with a 1956 film for which Brynner won an Academy Award. More successful revivals followed. In the early 1980s, Brynner starred in an extended national tour of the musical, culminating with a 1985 Broadway run, shortly before his death. The King and I saw another Broadway revival in 1996, with Lou Diamond Phillips as the King and Donna Murphy as Anna, and a 2000 London production.

The King and I opened on Broadway on March 29, 1951, with a wide expectation of a hit. Both Hammerstein and Rodgers professed to be worried. The composer complained that most people were not concerned about whether the show was good, but whether it was better than South Pacific. Even the weather cooperated?heavy rain in New York stopped a few minutes before curtain, allowing the royalty of Broadway to arrive dry at the St. James Theatre.[44] Margaret Landon, author of the book on which the musical was based, was not invited to opening night.[45] Brynner turned in an outstanding performance that night, nearly stealing the show. Lawrence knew that the company was nervous about her performance because of her illnesses. As Van Druten described her opening night performance, however: "She came on the stage with a new and dazzling quality, as if an extra power had been granted to the brilliance of her stage light. She was radiant and wonderful."[46] The rave reviews lifted Lawrence's spirits, and she expected a lengthy run as Anna, first on Broadway, then in the West End, and finally on film.[47] Lawrence won a Tony Award for her leading role, while Brynner won the award for best featured (that is, secondary) actor.[17] The production itself won the Tony for best musical, and designers Mielziner and Sharaff received Tony Awards.

The original London production opened on October 8, 1953 at the Theatre Royal, Drury Lane and was warmly received by both audiences and critics;[59] it ran for 946 performances.[60] The show was restaged by Jerome Whyte.[49] The cast featured Valerie Hobson, in her last role, as Anna;[61] Herbert Lom as the King; and Muriel Smith as Lady Thiang.[60] Martin Benson played the Kralahome,[49] a role he reprised in the 1956 film.[60] Eve Lister was a replacement for Hobson, and George Pastell replaced Lom during the long run.

The musical was filmed in 1956 with Brynner re-creating his role opposite Deborah Kerr. The film won 5 Academy Awards and was nominated for four more. Brynner won an Oscar as Best Actor for his portrayal, and Kerr was nominated as Best Actress.[105] Sharaff won for best costume design.[106] The film was directed by Walter Lang (who was also nominated for an Oscar) and choreographed by Robbins. Marni Nixon dubbed the singing voice of Anna, Rita Moreno played Tuptim, and other notable performers included Adiarte as Chulalongkorn and Benson as the Kralahome, reprising their stage roles, as did dancers Yuriko and de Lappe. Alan Mowbray appeared in the new role of the British Ambassador, while Sir Edward Ramsey (demoted to the Ambassador's aide) was played by Geoffrey Toone.[107][108] The movie was faithful to the stage version, and although it cut a few songs, reviews were enthusiastic. Thomas Hischak, in his The Rodgers and Hammerstein Encyclopedia, states: "It is generally agreed that the [movie] is the finest film adaptation of any R & H musical".