April 4 (UPI) -- On this date in history:
In 1841, President William Henry Harrison died of pneumonia after serving one month in office. He was the ninth President of the United States, and the first to die in office. He was succeeded by Vice President John Tyler, the first person to occupy the office without being elected to it.
In 1850, the city of Los Angeles was incorporated.
In 1887, Susanna Madora Salter was elected as the first female mayor in the United States -- in Argonia, Kan.
In 1933, the USS Akron, a U.S. Navy airship, is destroyed during a major storm off the coast of New Jersey. The tragedy claimed the lives of 73 of the 76 crewmen and passengers.
In 1949, representatives of 12 nations gathered in Washington to sign the North Atlantic Treaty, creating the NATO alliance.
In 1968, civil rights leader Martin Luther King, Jr. was assassinated as he stood on the balcony of the Lorraine Motel in Memphis Tenn. He was 39.
In 1975, Microsoft was founded by Bill Gates and Paul Allen.
In 1983, the space shuttle Challenger lifted off on its inaugural mission.
In 1991, Sen. John Heinz, R-Pa., and six others were killed in the midair collision of a chartered airplane and a helicopter that was inspecting the plane's landing gear near Philadelphia.
In 2005, the president of Kyrgyzstan, Askar Akayev, officially resigned. He had been driven out by a coup a month earlier.
In 2013, Pulitzer Prize-winning Chicago film critic Roger Ebert died after a long battle with cancer. He was 70.
In 2014, the United Nations announced that the millionth refugee from war-torn Syria had entered Lebanon.
In 2017, Syrian government forces kill dozens of civilians in a chemical attack in the rebel-held town of Khan Sheikhoun.
In 2019, the Church of Jesus Christ of Latter-day Saints reversed its policy denying the children of lesbian, gay, bisexual and transgender parents to be blessed as infants and baptized as members.