Leopold III (3 November 1901 – 25 September 1983) reigned as King of the Belgians from 1934 until 1951, when he abdicated in favour of the heir apparent, his son Baudouin. From 1944 until 1950, Leopold's brother, Charles, served as prince regent while Leopold was declared unable to rule. In 1950, the debate about whether Leopold could resume his royal functions provoked a political crisis known as the Royal Question.

Leopold was born in Brussels and succeeded to the throne of Belgium on 23 February 1934 following the death of his father, King Albert I. He was invested as Knight of the Order of the Golden Fleece in Spain in 1923, Grand Cross of the Order of the Tower and Sword (Portugal) in 1927 and Knight of the Order of the Garter (United Kingdom) in 1935.

Prince Leopold, Duke of Brabant, was sent by his father to Eton College in the United Kingdom in 1915. After the war, in 1919, the Duke visited the Old Mission and Saint Anthony Seminary in Santa Barbara, California. He married Princess Astrid of Sweden in a civil ceremony in on 4 November 1926, followed by a religious ceremony in Brussels on 10 November. The marriage produced three children:

On 29 August 1935, while the king and queen were driving along the winding, narrow roads near their villa at Küssnacht am Rigi, Schwyz, Switzerland, on the shores of Lake Lucerne, Leopold lost control of the car which plunged into the lake, killing Queen Astrid.

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