This was the name of two ruling queens of Portugal. It was also borne by the Habsburg queen Maria Theresa (1717-1780), whose inheritance of the domains of her father, the Holy Roman emperor Charles VI, began the War of the Austrian Succession.
As an English name it has been very popular since the Middle Ages. It was the top name for girls in England and Wales in the 1920s, 30s and 40s, but it declined in the latter half of the 20th century.
Other saints by this name include a queen of Scotland and a princess of Hungary. It was also borne by Queen Margaret I of Denmark, who united Denmark, Sweden, and Norway in the 14th century. Famous literary bearers include American writer Margaret Mitchell (1900-1949), the author of Gone with the Wind, and Canadian writer Margaret Atwood (1939-). Others include American anthropologist Margaret Mead (1901-1978) and British prime minister Margaret Thatcher (1925-2013).
The Cornish form of this name, Jennifer, has become popular in the English-speaking world.
As a given name, Diana has been regularly used since the Renaissance. It became more common in the English-speaking world following Walter Scott's novel Rob Roy (1817), which featured a character named Diana Vernon. It also appeared in George Meredith's novel Diana of the Crossways (1885). A notable bearer was the British royal Diana Spencer (1961-1997), the Princess of Wales.
In the Middle Ages this name was common in England due to the popularity of medieval tales about the Trojan War. It subsequently became rare, but was revived in the 20th century.