Timothy Leary was a clinical psychologist at Harvard, his advocacy for psychedelics (mainly LSD) got him both famous and fired. He is most well-known for the phrase “turn on, tune in, drop out.”
Leary was one of the leaders of the counter culture ‘revolution’ in the 1960s and Richard Nixon called him the most dangerous man in America.
You can find out more about his history on his Wikipedia page.
You can find his bibliography here.
Two experiments he did with LSD are often still cited. The first is the Concord Prison Experiment (giving prisoners psilocybin, later analysis says the recidivism was unchanged). The second is the Marsh Chapel Experiment – better known as the Good Friday Experiment – where divinity students were given psilocybin and reliably had spiritual experiences (follow-up research by Roland Griffiths did show this effect to be reliable).