Aspirin is a trade name for acetylsalicylic acid, a common analgesic.  The earliest known uses of the drug can be traced back to the Greek physician Hippocrates in the fifth century B.C.  He used powder extracted from the bark of willows to treat pain and reduce fever.

Salicin, the parent of the salicylate drug family, was successfully isolated in 1829 from willow bark.  Sodium salicylate, a predecessor to aspirin, was developed along with salicylic acid in 1875 as a pain reliever.

Sodium salicylate was not often popular though, as it has a habit of irritating the stomach.  However, in 1897, a man named Felix Hoffman changed the face of medicine forever.  Hoffman was a German chemist working for Bayer.  He had been using the common pain reliever of the time, sodium salicylate, to treat his father's arthritis.

The sodium salicylate caused his father the same stomach trouble it caused other people, so Felix decided to try and concoct a less acidic formula.  His work led to the synthesization of acetylsalicylic acid, or ASA.  This soon became the pain killer of choice for physicians around the globe.

Scientists never really understood the inner workings of the drug however.  It wasn't until the 1970's, when British pharmacologist John Vane, Ph.D. began work on aspirin that people began to understand how aspirin really works.  Vane and his colleagues found that aspirin inhibited the release of a hormone like substance called prostaglandin.  This chemical regulates certain body functions, such as blood vessel elasticity and changing the functions of blood platelets.  Thus can aspirin affect blood clotting and ease inflammation.