David E. Nichols is a researcher (specifically pharmacologist and medicinal chemist) at Purdue University (semi-retired in 2012). His psychedelics work has been ongoing since 1969.
Next to research (papers linked below), he is also the founding president of the Heffter Research Institute.
He sits on the advisory board of the MIND Foundation.
Learn more on his Wikipedia page.
Not to be confused with Charles D. Nichols, whom he often collaborates with.