Mircea Eliade (1907–1986) was a Romanian historian of religion, fiction writer, philosopher, and professor at the University of Chicago.
He was one of the leading writers about the mystery of the religious experience, and developed insights and methods in the field of religious studies.
His theory that hierophanies form the basis of religion, splitting the human experience of reality into sacred and profane space and time, has proven to be a seminal idea.
One of his most influential contributions to religious studies was his theory of Eternal Return, which holds that myths and rituals do not simply commemorate hierophanies, but, at least to the minds of the religious, actually participate in them.
Besides, I find Eliade was even more an expert of shamanism research than just an expert of the religious and numinous experience; his religious studies have to be seen culminating in his long-year research on shamanism in its dimension as a set of techniques that provoke and facilitate religious ecstacy, a state of deep inner communion with all-that-is.
His 1964 book is still a leading bestseller for the researcher. While some of his theories, as for example his opinion that psychedelics for provoking ecstasy were only used by decadent tribal peoples, were contradicted by other (younger) researchers, overall and from an academic perspective, his book is an absolute must-read for all and everyone who want to get a feel what the shamanic experience is about in all its incredible variety among tribal peoples around the world.