- 753 BC Romulus and Remus found Rome (traditional date).
- 1526 Battle at Panipat: Central Asian conqueror Babur defeats Sultan Ibrahim Lodi, establishing the Mughal Empire in India
- 1792 Brazilian revolutionary Tiradentes, is hanged, drawn and quartered in Rio de Janeiro
- 1863 Bahá'u'lláh, founder of the Bahá'í Faith, enters gardens of Rivden, near Baghdad. Makes the declaration of aha'u'llah during 12 days spent there
- 1918 World War I: German fighter ace Baron Manfred von Richthofen "The Red Baron", shot down and killed over Vaux sur Somme in France, Canadian pilot Arthur Roy Brown credited with the kill
- 1989 Thousands of Chinese crowd into Beijing's Tiananmen Square cheering students demanding greater political freedom
Elvis Presley's 1st hit record, "Heartbreak Hotel", becomes #1
On April 21, 1956