Terence Kemp McKenna (November 16, 1946 – April 3, 2000) was an American ethnobotanist and mystic who advocated for the responsible use of naturally occurring psychedelic plants. He spoke and wrote about a variety of subjects, including psychedelic drugs, plant-based entheogens, shamanism, metaphysics, alchemy, language, philosophy, culture, technology, environmentalism, and the theoretical origins of human consciousness. He was called the "Timothy Leary of the '90s", "one of the leading authorities on the ontological foundations of shamanism", and the "intellectual voice of rave culture".
McKenna formulated a "novelty theory" regarding the nature of time based on fractal patterns, which he claimed to discover in the I Ching, and predicting a transition of consciousness in the year 2012. Despite the pseudoscientific nature of novelty theory, promotion of its ideas and its connection to the Maya calendar helped fuel widespread beliefs about 2012 eschatology.