Jacqueline Lee Kennedy Onassis (née Bouvier /ˈbuːvieɪ/; July 28, 1929 – May 19, 1994), also known as Jackie O, was the first lady of the United States from 1961 to 1963, as the wife of President John F. Kennedy. During her lifetime, she was regarded as an international icon for her unique fashion choices, and her work as a cultural ambassador of the United States made her popular globally.

After studying history and art at Vassar College and graduating with a Bachelor of Arts in French literature from George Washington University in 1951, Bouvier started working for the Washington Times-Herald as an inquiring photographer. The following year, she met then-Congressman John F. Kennedy of Massachusetts at a dinner party in Washington. He was elected to the Senate that same year, and the couple married on September 12, 1953, in Newport, Rhode Island. They had four children, two of whom died in infancy. Following her husband's election to the presidency in 1960, Kennedy was known for her highly publicized restoration of the White House and emphasis on arts and culture as well as for her style. She also traveled to many countries where her fluency in foreign languages and history made her very popular. At age 33, she was named Time magazine's Woman of the Year in 1962.

After her husband's assassination and funeral in 1963, Kennedy and her children largely withdrew from public view. In 1968, she married Greek shipping magnate Aristotle Onassis, which caused controversy. Following Onassis's death in 1975, she had a career as a book editor in New York City, first at Viking Press and then at Doubleday, and worked to restore her public image. Even after her death, she ranks as one of the most popular and recognizable First Ladies in American history, and in 1999, she was placed on the list of Gallup's Most-Admired Men and Women of the 20th century. She died in 1994 and is buried at Arlington National Cemetery alongside President Kennedy and two of their children, one stillborn and one who died shortly after birth. Surveys of historians conducted periodically by the Siena College Research Institute since 1982 have also consistently found Kennedy Onassis to rank among the most highly regarded First Ladies.

Jacqueline Lee Bouvier was born on July 28, 1929, at Southampton Hospital in Southampton, New York, to Wall Street stockbroker John Vernou "Black Jack" Bouvier III and socialite Janet Norton Lee. Her mother was of Irish descent, and her father had French, Scottish, and English ancestry. Named after her father, she was baptized at the Church of St. Ignatius Loyola in Manhattan and raised in the Roman Catholic faith. Caroline Lee, her younger sister, was born four years later on March 3, 1933.

Jacqueline Bouvier spent her early childhood years in Manhattan and at Lasata, the Bouviers' country estate in East Hampton on Long Island. She looked up to her father, who likewise favored her over her sister, calling his elder child "the most beautiful daughter a man ever had". Biographer Tina Santi Flaherty reports Jacqueline's early confidence in herself, seeing a link to her father's praise and positive attitude to her, and her sister Lee Radziwill stated that Jacqueline would not have gained her "independence and individuality" had it not been for the relationship she had with their father and paternal grandfather, John Vernou Bouvier Jr. From an early age, Jacqueline was an enthusiastic equestrian and successfully competed in the sport, and horse-riding remained a lifelong passion. She took ballet lessons, was an avid reader, and excelled at learning foreign languages, including French, Spanish, and Italian. French was particularly emphasized in her upbringing.

In 1935, Jacqueline Bouvier was enrolled in Manhattan's Chapin School, where she attended grades 1–7. She was a bright student but often misbehaved; one of her teachers described her as "a darling child, the prettiest little girl, very clever, very artistic, and full of the devil". Her mother attributed this behavior to her finishing her assignments ahead of classmates and then acting out in boredom. Her behavior improved after the headmistress warned her that none of her positive qualities would matter if she did not behave.

The marriage of the Bouviers was strained by the father's alcoholism and extramarital affairs; the family had also struggled with financial difficulties following the Wall Street Crash of 1929. They separated in 1936 and divorced four years later, with the press publishing intimate details of the split. According to her cousin John H. Davis, Jacqueline was deeply affected by the divorce and subsequently had a "tendency to withdraw frequently into a private world of her own." When their mother married stockbroker and lawyer Hugh D. Auchincloss Jr., the Bouvier sisters did not attend the ceremony because it was arranged quickly and travel was restricted due to World War II. They gained three stepsiblings from Auchincloss's previous marriages, Hugh "Yusha" Auchincloss III, Thomas Gore Auchincloss, and Nina Gore Auchincloss. Jacqueline formed the closest bond with Yusha, who became one of her most trusted confidants. The marriage later produced two more children, Janet Jennings Auchincloss in 1945 and James Lee Auchincloss in 1947.

After the remarriage, Auchincloss's Merrywood estate in McLean, Virginia, became the Bouvier sisters' primary residence, although they also spent time at his other estate, Hammersmith Farm in Newport, Rhode Island, and in their father's homes in New York City and Long Island. Although she retained a relationship with her father, Jacqueline Bouvier also regarded her stepfather as a close paternal figure. He gave her a stable environment and the pampered childhood she otherwise would have never experienced. While adjusting to her mother's remarriage, she sometimes felt like an outsider in the WASP social circle of the Auchinclosses, attributing the feeling to her being Catholic as well as being a child of divorce, which was not common in that social group at that time.