May 20 is the 140th day of the year (141st in leap years) in the Gregorian calendar. There are 225 days remaining until the end of the year.
- 325 - The First Council of Nicaea – the first Ecumenical Council of the Christian Church is held.
- 526 - An earthquake kills about 300,000 people in Syria and Antiochia.
- 685 - The Battle of Dunnichen or Nechtansmere is fought between a Pictish army under King Bridei III and the invading Northumbrians under King Ecgfrith, who are decisively defeated.
- 1217 - The Second Battle of Lincoln is fought near Lincoln, England, resulting in the defeat of Prince Louis of France by William Marshal, 2nd Earl of Pembroke.
- 1293 - King Sancho IV of Castile creates the Study of General Schools of Alcalá.
- 1497 - John Cabot sets sail from Bristol, England, on his ship Matthew looking for a route to the west (other documents give a May 2 date).
- 1498 - Portuguese explorer Vasco da Gama arrives at Kozhikode (previously known as Calicut), India.
- 1521 - Battle of Pampeluna: Ignatius Loyola is seriously wounded.
- 1570 - Cartographer Abraham Ortelius issues the first modern atlas.
- 1609 - Shakespeare's Sonnets are first published in London, perhaps illicitly, by the publisher Thomas Thorpe.
- 1631 - The city of Magdeburg in Germany is seized by forces of the Holy Roman Empire and most of its inhabitants massacred, in one of the bloodiest incidents of the Thirty Years' War.
- 1813 - Napoleon Bonaparte leads his French troops into the Battle of Bautzen in Saxony, Germany, against the combined armies of Russia and Prussia. The battle ends the next day with a French victory.
- 1835 - Otto is named the first modern king of Greece.
- 1840 - York Minster was badly damaged by fire
- 1845 - HMS Erebus and HMS Terror with 134 men under John Franklin sail from the River Thames in England, beginning a disastrous expedition to find the Northwest Passage. All hands are lost.
- 1861 - American Civil War: The state of Kentucky proclaims its neutrality, which will last until September 3 when Confederate forces enter the state.
- 1862 - U.S. President Abraham Lincoln signs the Homestead Act into law.
- 1864 - American Civil War: Battle of Ware Bottom Church - in the Virginia Bermuda Hundred Campaign, 10,000 troops fight in this Confederate victory.
- 1873 - Levi Strauss and Jacob Davis receive a U.S. patent for blue jeans with copper rivets.
- 1882 - The Triple Alliance between Germany, Austria-Hungary and Italy is formed.
- 1883 - Krakatoa begins to erupt. The volcano's final and most notable explosion occurs on August 26.
- 1891 - History of cinema: The first public display of Thomas Edison's prototype kinetoscope.
- 1896 - The six ton chandelier of the Palais Garnier falls on the crowd resulting in the death of one and the injury of many others.
- 1902 - Cuba gains independence from the United States. Tomás Estrada Palma becomes the first President of Cuba.
- 1916 - The Saturday Evening Post publishes its first cover with a Norman Rockwell painting ("Boy with Baby Carriage").
- 1916 - The small town of Codell, Kansas is struck by a tornado. Incredibly, the same town was also hit in 1917 and 1918 on the exact same date.
- 1920 - Montreal, Quebec radio station XWA broadcasts the first regularly scheduled radio programming in North America.
- 1927 - By the Treaty of Jedda, the United Kingdom recognizes the sovereignty of King Ibn Saud in the Kingdoms of Hejaz and Nejd, which later merged to become the Kingdom of Saudi Arabia.
- 1927 - At 07:52 Charles Lindbergh takes off from Roosevelt Field in Long Island, New York, on the world's first solo non-stop flight across the Atlantic Ocean, touching down at Le Bourget Field in Paris at 22:22 the next day.
- 1932 - Amelia Earhart takes off from Newfoundland to begin the world's first solo nonstop flight across the Atlantic Ocean by a female pilot, landing in Ireland the next day.
- 1940 - Holocaust: The first prisoners arrive at a new concentration camp at Auschwitz.
- 1941 - World War II: Battle of Crete – German paratroops invade Crete.
- 1949 - In the United States, the Armed Forces Security Agency, the predecessor to the National Security Agency, is established.
- 1949 - The Kuomintang regime declares Taiwan is under martial law.
- 1954 - Chiang Kai-shek is selected for another term as President of the Republic of China by the National Assembly.
- 1956 - In Operation Redwing, (shot Cherokee), the first United States airborne hydrogen bomb is dropped over Bikini Atoll in the Pacific Ocean;
- 1965 - PIA Flight 705, a Pakistan International Airlines Boeing 720 - 040 B crashes while descending to land at Cairo International Airport, killing 119 of the 125 passengers and crew.
- 1969 - The Battle of Hamburger Hill in Vietnam ends.
- 1980 - In a referendum in Quebec, the population rejects by a 60% vote the proposal from its government to move towards independence from Canada.
- 1983 - First publications of the discovery of the HIV virus that causes AIDS in the journal Science by Luc Montagnier and Robert Gallo individually.
- 1985 - Radio Martí, part of the Voice of America service, begins broadcasting to Cuba.
- 1989 - The Chinese authorities declare martial law in the face of pro-democracy demonstrations, setting the scene for the Tiananmen Square massacre.
- 1990 - The first post-Communist presidential and parliamentary elections are held in Romania.
- 1995 - In a second referendum in Quebec, the population rejects by a slight majority the proposal from its government to move towards independence from Canada.
- 1996 - Gay rights: The Supreme Court of the United States rules in Romer v. Evans against a law that would have prevented any city, town or county in the state of Colorado from taking any legislative, executive, or judicial action to protect the rights of gays and lesbians.
- 2002 - The independence of East Timor is recognized by Portugal, formally ending 23 years of Indonesian rule and 3 years of provisional UN administration (Portugal itself was the former colonizer of East Timor until 1976).
- 1315 - Bonne of Luxembourg, wife of John II of France (d. 1349)
- 1470 - Pietro Bembo, Italian cardinal (d. 1547)
- 1554 - Paolo Bellasio, Italian composer (d. 1594)
- 1593 - Salomo Glassius, German theologian (d. 1656)
- 1660 - Andreas Schlüter, German sculptor (d. 1714)
- 1663 - William Bradford, British-born printer (d. 1752)
- 1706 - Seth Pomeroy, American gunsmith and soldier (d. 1777)
- 1726 - Francis Cotes, English painter (d. 1770)
- 1737 - William Petty Fitzmaurice, British statesman (d. 1805)
- 1759 - William Thornton, West Indian-born architect (d. 1828)
- 1768 - Dolley Madison, First Lady of the United States (d. 1849)
- 1769 - Andreas Vokos Miaoulis, Greek admiral and politician (d. 1835)
- 1772 - Sir William Congreve, English inventor (d. 1828)
- 1799 - Honoré de Balzac, French novelist (d. 1850)
- 1806 - John Stuart Mill, English philosopher (d. 1873)
- 1818 - William Fargo, co-founder of Wells, Fargo & Company (d. 1881)
- 1822 - Frédéric Passy, French economist, Nobel laureate (d. 1912)
- 1830 - Hector Malot, French writer (d. 1907)
- 1838 - Jules Méline, French statesman (d. 1925)
- 1851 - Emil Berliner, German-born recording pioneer (d. 1929)
- 1860 - Eduard Buchner, German chemist, Nobel laureate (d. 1917)
- 1882 - Sigrid Undset, Norwegian author, Nobel laureate (d. 1949)
- 1883 - King Faisal I of Iraq (d. 1933)
- 1894 - Chandrashekarendra Saraswati, Indian Hindu sage, Jivanmukta (d. 1994)
- 1895 - R. J. (Reginald Joseph) Mitchell, British aircraft designer (d. 1937)
- 1897 - Diego Abad de Santillán, Spanish anarchist (d. 1983)
- 1899 - Alexander Deyneka, Ukrainian painter (d. 1969)
- 1899 - John Marshall Harlan II, Justice of the U.S. Supreme Court (d. 1971)
- 1901 - Max Euwe, Dutch chess player (d. 1981)
- 1906 - Giuseppe Siri, Italian Catholic cardinal (d. 1989)
- 1908 - James Stewart, American actor (d. 1997)
- 1911 - Gardner Fox, American writer (d. 1986)
- 1913 - William Hewlett, American engineer (d. 2001)
- 1914 - Corneliu Coposu, Romanian politician (d. 1995)
- 1914 - Hideko Maehata, Japanese swimmer (d. 1995)
- 1915 - Moshe Dayan, Israeli general (d. 1981)
- 1916 - Trebisonda Valla, Italian athlete (d. 2006)
- 1916 - Alexei Petrovich Maresiev, Russian flying ace (d. 2001)
- 1917 - Guy Favreau, French Canadian lawyer (d. 1967)
- 1917 - Bergur Sigurbjörnsson, Icelandic politician (d. 2005)
- 1918 - Edward B. Lewis, American geneticist, Nobel laureate (d. 2004)
- 1919 - Gerhard Barkhorn, German fighter pilot (d. 1983)
- 1919 - George Gobel, American comedian (d. 1991)
- 1920 - John Cruickshank, Scottish airman, Victoria Cross recipient
- 1920 - Betty Driver, English singer and actress
- 1921 - Wolfgang Borchert, German writer (d. 1947)
- 1921 - Hal Newhouser, American baseball player (d. 1998)
- 1925 - Chester Ludgin, American baritone (d. 2003)
- 1926 - Bob Sweikert, American race car driver (d. 1956)
- 1926 - John Lucarotti, TV writer (d. 1994)
- 1927 - Bud Grant, American football coach
- 1927 - Franciszek Macharski, Polish Cardinal
- 1927 - David Hedison, American actor
- 1930 - Sam Etcheverry, American football player and coach
- 1931 - Ken Boyer, American baseball player (d. 1982)
- 1931 - Paul Evans, American furniture designer and sculptor (d. 1987)
- 1932 - Bob Florence, American jazz pianist, composer, arranger (d. 2008)
- 1936 - Anthony Zerbe, American actor
- 1936 - Lee "Scratch" Perry, Jamaican reggae and dub artist
- 1938 - Marinella, Greek singer and actress
- 1940 - Stan Mikita, Slovak-born ice hockey player
- 1940 - Sadaharu Oh, Japanese baseball player
- 1940 - Shorty Long, American musician (d. 1969)
- 1941 - Goh Chok Tong, Singaporean Senior Minister
- 1941 - John Strasberg, American actor
- 1941 - Manuel Isaias Lopez, Mexican child psychiatrist
- 1942 - Carlos Hathcock, American Marine sniper (d. 1999)
- 1942 - Jill Jackson, American singer
- 1943 - Al Bano, Italian singer
- 1944 - Joe Cocker, British singer
- 1944 - Boudewijn de Groot, Dutch singer
- 1944 - Dietrich Mateschitz, Austrian businessman
- 1945 - Vladimiro Montesinos, Peruvian politician
- 1946 - Cher, American singer
- 1947 - Greg Dyke, British broadcast executive
- 1949 - Dave Thomas, Canadian comedian & actor
- 1950 - Yvon Lambert, French Canadian ice hockey player
- 1950 - Reinaldo Merlo, Argentine footballer
- 1951 - Mike Crapo, American politician
- 1952 - Roger Milla, Cameroonian footballer
- 1953 - Robert Doyle, Australian politician
- 1954 - Guy Hoffman, American musician (Violent Femmes)
- 1954 - David Paterson, American politician
- 1954 - Cindy Hensley McCain, wife of John McCain
- 1954 - Robert Van de Walle, Belgian judoka
- 1955 - Zbigniew Preisner, Polish film composer
- 1956 - Ingvar Ambjørnsen, Norwegian author
- 1956 - Dean Butler, American actor
- 1956 - William Michaelian, American novelist and poet
- 1958 - Ron Reagan, American talk show host
- 1958 - Jane Wiedlin, American singer (The Go-Go's)
- 1959 - Israel Kamakawiwo'ole, American singer (d. 1997)
- 1959 - Bronson Pinchot, American actor
- 1960 - John Billingsley, American actor
- 1960 - Chuck Brodsky, American musician
- 1960 - Tony Goldwyn, American actor
- 1961 - Clive Allen, English footballer
- 1962 - Mike Jeffries, American soccer coach
- 1963 - David Wells, American baseball player
- 1965 - Ted Allen, American television host
- 1966 - Mindy Cohn, American actress
- 1966 - Dan Abrams, American TV reporter
- 1966 - Gina Ravera, American actress
- 1967 - Gabriele Muccino, Italian film director
- 1967 - Ramzi Yousef, Kuwaiti-born Pakistani terrorist
- 1967 - Pavlos, Crown Prince of Greece
- 1968 - Timothy Olyphant, American actor
- 1968 - Waisale Serevi, Fijian rugby union and rugby sevens footballer
- 1969 - Brian Gerard James, American professional wrestler
- 1970 - Louis Theroux, British television presenter
- 1970 - Terrell Brandon, American basketball player
- 1971 - Šárka Kašpárková, Czech athlete
- 1971 - Tony Stewart, American race car driver
- 1972 - Tina Hobley, British television actress
- 1972 - Busta Rhymes, American singer and rapper
- 1973 - Elsa Lunghini, French singer and actress
- 1975 - Isaac Gálvez, Spanish cyclist (d. 2006)
- 1975 - Mark Zupan, American quadriplegic rugby player
- 1976 - Ramón Hernández, Venezuelan baseball player
- 1976 - Tomoya Satozaki, Japanese baseball player
- 1977 - Matt Czuchry, American actor
- 1977 - Chad Muska, American Skateboarder for Element Skateboards
- 1977 - Leonardo Noeren Franco, Argentine footballer
- 1977 - Miriam Parrish, American television actress
- 1977 - Angela Goethals, American actress
- 1977 - Vesa Toskala, Finnish ice hockey player
- 1977 - Tiger Tyson, American gay-pornographic actor
- 1980 - Austin Kearns, American Baseball player
- 1981 - Iker Casillas, Spanish footballer
- 1981 - Calico Cooper, American actress and dancer
- 1981 - Lindsay Taylor, American basketball player
- 1981 - Mark Winterbottom, Australian racing driver
- 1982 - Petr Čech, Czech footballer
- 1982 - Imran Farhat, Pakistani cricketer
- 1983 - Jr. NTR, Indian film actor
- 1984 - Kenny Vasoli, American singer
- 1986 - Dexter Blackstock, English footballer
- 1988 - Carla Humphries, Filipina actress
- 1993 - Caroline Zhang, American figure skater
- 685 - King Ecgfrith of Northumbria (b. 645)
- 1277 - Pope John XXI (b. 1215)
- 1285 - John II of Jerusalem, King of Cyprus (b. 1259)
- 1444 - Saint Bernardino of Siena, Italian Franciscan missionary (b. 1380)
- 1503 - Lorenzo de Medici, Italian patron (b. 1463)
- 1506 - Christopher Columbus, Italian explorer (b. 1451)
- 1550 - Ashikaga Yoshiharu, Japanese shogun (b. 1510)
- 1622 - Osman II, Ottoman Sultan (b. 1604)
- 1648 - King Wladislaus IV of Poland (b. 1595)
- 1677 - George Digby, 2nd Earl of Bristol, British statesman (b. 1612)
- 1713 - Thomas Sprat, English writer (b. 1635)
- 1717 - John Trevor, British statesman (b. 1637)
- 1722 - Sébastien Vaillant, French botanist (b. 1669)
- 1732 - Thomas Boston, Scottish church leader (b. 1676)
- 1782 - William Emerson, British mathematician (b. 1701)
- 1793 - Charles Bonnet, Swiss naturalist (b. 1720)
- 1812 - Count Hieronymus von Colloredo, Archbishop of Salzburg (b. 1732)
- 1825 - Papaflessas, Greek priest and government official (b. 1788)
- 1834 - Gilbert du Motier, French statesman (b. 1757)
- 1841 - Joseph Blanco White, British theologian (b. 1775)
- 1873 - Sir George-Étienne Cartier, French-Canadian statesman (b. 1814)
- 1896 - Clara Schumann, German pianist and composer (b. 1819)
- 1909 - Ernest Hogan, blackface comedian and musician (b. 1859)
- 1917 - Philipp von Ferrary, Italian philatelist (b. 1850)
- 1917 - Valentine Fleming, Scottish politician (b. 1887)
- 1940 - Verner von Heidenstam, Swedish writer, Nobel laureate (b. 1859)
- 1946 - Jacob Ellehammer, Danish inventor (b. 1871)
- 1947 - Philipp Lenard, Austrian physicist, Nobel laureate (b. 1862)
- 1949 - Randolph West, American biochemist, known for the Dakin-West reaction (b. 1890)
- 1956 - Max Beerbohm, English theater critic (b. 1872)
- 1961 - Josef "Pips" Priller, German fighter ace (b. 1915)
- 1971 - Waldo Williams, Welsh poet (b. 1904)
- 1973 - Jarno Saarinen, Finnish motorcycle racer (b. 1945)
- 1975 - Barbara Hepworth, British sculptor (b. 1903)
- 1976 - Syd Howe, Canadian ice hockey player (b. 1911)
- 1976 - Zelmar Michelini, Uruguayan politician, member of the Christian-Democrat party, and Héctor Gutiérrez Ruiz "disappeared"
- 1989 - John Hicks, English economist, Nobel laureate (b. 1904)
- 1989 - Gilda Radner, American comedian and actress (b. 1946)
- 1992 - Roger Keith Coleman, American convict
- 1996 - Jon Pertwee, British actor (b. 1919)
- 2000 - Jean Pierre Rampal, French flutist (b. 1922)
- 2000 - Malik Sealy, American basketball player (b. 1970)
- 2001 - Renato Carosone, Italian musician (b. 1920)
- 2002 - Stephen Jay Gould, American paleontologist (b. 1941)
- 2005 - Paul Ricoeur, French philosopher (b. 1913)
- 2005 - William Seawell, United States Army Brigadier General (b. 1918)
- 2007 - Norman Von Nida, Australian golfer (b. 1914)
- 2008 - Hamilton Jordan, former Carter White House Chief of Staff (b. 1944)
Saints in the Roman Catholic Church:
