Here’s the quick version of the story of his discovery of LSD, excerpted from Wired News:
Hofmann’s most famous discovery happened on April 16, 1943. He was researching the synthesis of a lysergic acid compound, LSD-25, when he inadvertently absorbed a bit through his fingertips. Intrigued by the effect it had on his perception, Hofmann decided further exploration was warranted. Three days later, on April 19, he ingested 250 micrograms of LSD, embarking on the first full-fledged acid trip. That day became known among LSD fans as “bicycle day” because Hofmann began experiencing the drug’s intense effects on his bicycle trip home from the lab.
For more on Dr. Hofmann’s life and passing, here are some links:
In tribute to Dr. Hofmann, here’s an excellent video treatment of William Shatner’s cover of Lucy in the Sky with Diamonds, complete with kitschy Star Trek and I Love Lucy graphics: