Aga Khan IV

Karim al-Husseini was born in Geneva, Switzerland, on 13 December 1936, the eldest son of Aly Khan (1911–1960) and his first wife, Taj-ud-dawlah Aga Khan (formerly Joan Yarde-Buller, 1908–1997). His mother was the eldest daughter of the British peer John Yarde-Buller, 3rd Baron Churston.

He was declared healthy despite being born prematurely. His brother, Amyn Aga Khan, was born a year later in 1937. In 1949, his parents divorced in part due to his father's extramarital affairs, and shortly after, his father married American actress Rita Hayworth—with whom he had a daughter, Yasmin Aga Khan, the half-sister of al-Husseini.

He also had a half-brother, Patrick Benjamin Guinness (1931–1965), from his mother's first marriage, as Joan Yarde-Buller was previously married to Loel Guinness of the banking Guinnesses.

Karim spent the years during World War II in Nairobi, Kenya, where his early education was through private tutoring. He later attended the Institut Le Rosey in Switzerland for nine years where he achieved, in his words, "fair grades". He was admitted to the Massachusetts Institute of Technology where he wanted to study science, but his grandfather, Aga Khan III, vetoed the decision. Instead he attended Harvard University, where he was elected a member of The Delphic Club and majored in Islamic history.

When his grandfather died, he was thrust into the position of the Aga Khan. At the time of his accession to the Imamate in 1957, Karim was a university student. Reflecting on the transition, he later stated that he had to set aside plans for further academic study in order to assume his new responsibilities as Imam. He graduated from Harvard University in 1959, two years after ascending the Imamate, with a Bachelor of Arts degree in history (with Cum Laude honours) and his varsity H for the Harvard Crimson men's soccer team.

He was a competitive downhill skier, representing Great Britain at the FIS Alpine World Ski Championships 1962 and then Iran in the 1964 Winter Olympics.

Thoroughbred horse racing

Al-Husseini's racing horse businesses brought in considerable income. He owned and operated the largest horse racing and breeding operation in France, the French horse auction house, Arqana, Gilltown Stud near Kilcullen in Ireland, and other breeding/stud farms in Europe.

He operated a large horse racing and breeding operation at his estate Aiglemont, in the town of Gouvieux in the Picardy region of France – about 4 kilometres (2+1⁄2 miles) west of the Chantilly Racecourse. In 1977, he paid £1.3 million for the bloodstock owned by Anna Dupré and in 1978, £4.7 million for the bloodstock of Marcel Boussac. He was said to be France's most influential owner-breeder and record winner of The Prix de Diane, sometimes referred to as the French Oaks.

Al-Husseini owned Gilltown Stud near Kilcullen, Ireland, and the Haras de Bonneval breeding farm at Le Mesnil-Mauger in France. In March 2005, he purchased the Calvados stud farms, the Haras d'Ouilly in Pont-d'Ouilly and the Haras de Val-Henry in Livarot. Haras d'Ouilly had been owned by such horsemen as the Duc Decazes, François Dupré, and Jean-Luc Lagardère.

In 2006, he became the majority shareholder of French horse auction house Arqana.

On 27 October 2009 it was announced that Sea the Stars, regarded by many as one of the greatest racehorses of all time, would stand stud at his Gilltown Stud in Ireland.

His unbeaten homebred filly, Zarkava, won the 2008 Prix de l'Arc de Triomphe. His homebred colt, Harzand, won the 2016 Epsom Derby and the 2016 Irish Derby.

Al-Husseini was the lead owner of Shergar, the Irish racehorse that was kidnapped from Ballymany stud farm in County Kildare, Ireland, by masked men in 1983 and held for ransom. He and the other co-owners refused to pay a ransom, and the horse was not recovered. Following the abduction of Shergar in 1983, al-Husseini, law enforcement, and members of the public suspected the Provisional Irish Republican Army (IRA), although the group denied involvement. In 1999, former IRA member Sean O'Callaghan claimed in his autobiography that the IRA had carried out the abduction. Shergar had become a prominent symbol in Ireland, and the incident prompted public backlash, including among individuals sympathetic to the republican cause.

He avoided most parties and never appeared in gossip columns. In 1969, al-Husseini married former British model Sarah Frances Croker Poole, who assumed the name Salimah Aga Khan upon marrying him. Sarah Frances was a divorcee, having previously been married to Lord James Charles Crichton-Stuart, third son of John Crichton-Stuart, 5th Marquess of Bute.

The wedding ceremonies were held on 22 October 1969 (civil) and 28 October 1969 (religious) at Karim Aga Khan's home in Paris. Al-Husseini and Begum Salimah had one daughter and two sons together, Zahra Aga Khan (born 18 September 1970), Rahim Aga Khan (born 12 October 1971), and Hussain Aga Khan (born 10 April 1974). By 1984, al-Husseini and Salimah had taken to living separate lives. In 1994, the couple's divorce was made public.

On 30 May 1998, al-Husseini married Gabriele Renate Thyssen at his residence, Château de Aiglemont, in Gouvieux, France. Upon marriage, she assumed the name Inaara Aga Khan. Thyssen, born in 1963, had previously been married to Prince Karl Emich of Leiningen, with whom she had a daughter, Teresa.

The couple had one son, Aly Muhammad Aga Khan, born on 7 March 2000. They announced their intention to divorce in October 2004. A divorce settlement was reached in the French courts in September 2011, with the settlement amount finalised in March 2014.

Al-Husseini was involved in competitive yachting and maritime sports. In 1967, he founded the Yacht Club Costa Smeralda in Porto Cervo, Sardinia, and served as its president for several decades. The club became known for hosting international sailing events.

He also owned multiple yachts, including Alamshar, a 164-foot vessel named after one of his racehorses. Media reports estimated its cost at approximately £100 million.Al-Husseini owned Bombardier jets. In 2005, it was reported that he owned a Bombardier Global Express and another transcontinental jet.