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Popular and acclaimed physicist and mathematician Stephen Hawking was rushed to the hospital in serious condition this morning, having "been unwell for a couple of weeks," according to a spokesman.

Hawking, who suffers from ALS and is almost completely paralyzed, is one of the most influential scientific minds of our time, in both academia and mainstream popular culture. His smash hit 1988 book A Brief History of Time brought musings on string theory, black holes, and other mysteries of cosmology to the forefront of pop science, selling some nine million copies worldwide. As a professor of mathematics and theoretical physics at Cambridge, Hawking has earned awards and recognition for his work on black hole radiation and the theory of relativity, among other topics.

Despite his physical limitations, Hawking has been an tireless and enduring cultural icon—penning a children's book, making many speaking engagements, even popping up on several episodes of The Simpsons. He's rooted almost somewhere between scientist and philosopher, in the same vein of his late and frequent debate partner, astronomer and author Carl Sagan.

Hawking is set to retire from Cambridge at the close of this academic year.