On this day in history, April 4
1581 – Francis Drake is knighted for completing a circumnavigation of the world.
1721 – Sir Robert Walpole takes office as the first Prime Minister of the United Kingdom under King George I.
1818 – The United States Congress adopts the flag of the United States with 13 red and white stripes and one star for each state (then 20).
1841 – William Henry Harrison dies of pneumonia becoming the first President of the United States to die in office and with the shortest term served.
1850 – Los Angeles, California is incorporated as a city.
1866 – Alexander II of Russia narrowly escapes an assassination attempt by Dmitry Karakozov in the city of Kiev.
1873 – The Kennel Club is founded, the oldest and first official registry of purebred dogs in the world.
1949 – Twelve nations sign the North Atlantic Treaty creating the North Atlantic Treaty Organization.
1964 – The Beatles occupy the top five positions on the Billboard Hot 100 pop chart.
1968 – Martin Luther King, Jr. is assassinated by James Earl Ray at a motel in Memphis, Tennessee.
1968 – Apollo program: NASA launches Apollo 6.
1969 – Dr. Denton Cooley implants the first temporary artificial heart.
1973 – The World Trade Center in New York is officially dedicated.
1975 – Microsoft is founded as a partnership between Bill Gates and Paul Allen in Albuquerque, New Mexico
1983 – Space Shuttle Challenger makes its maiden voyage into space (STS-6).
1984 – President Ronald Reagan calls for an international ban on chemical weapons.
1988 – Governor Evan Mecham of Arizona is convicted in his impeachment trial and removed from office.