The Spanish flu, also known as the 1918 flu pandemic, killed fifty million people globally. It was an abnormally deadly influenza pandemic, caused by the H1N1 influenza A virus. It lasted from February of 1918 to April of 1920. Hitting in four successive waves, this pandemic struck approximately a third of the world's population at the time (500,000,000 people). Click here to enlarge the above image.