This early researcher did a study that seemed to suggest that people deprived of rem sleep would become paranoid, seemingly mentally ill, from lack of this one stage of sleep

The correct answer to this open question is the following.

William Charles Dement was the early researcher that did a study that seemed to suggest that people deprived of REM sleep would become paranoid, seemingly mentally ill, from lack of this one stage of sleep.

He is a US scientist and researcher for the University of Stanford in Palo Alto, California. Indeed, he founded the Sleep Research Center to do the thing that is his passion: to study sleep disorders and help find alternatives to people who suffer from lack of sleep.