Hoffman was a visionary chemist who synthesized, among other things, LSD. He's known for his work using psychedelics in a therapeutic sense as well. His wife Anita is well known in the field as well, and he's been the speaker of honor numerous times at the World Psychedelic Forum in Basel, Switzerland.
More or less him and his wife were the pioneers of using psychedelics for therapeutic purposes and for getting governments across the world to re-institute research with psychedelics. Very cool guy. He always stated that his greatest regret in life was the misuse of his "problem child" LSD.