The Greek philosopher and mathematician Pythagoras believed that the spirits of the dead were carried off by the ocean, until they reached the horizon and met the rising moon. And thus, the moon is where they permanently reside.
Over the years, various craters on the moon have been named after historical personages. This one is named Pythagoras.
The story goes that Hippasus discovered irrational numbers when trying to represent the square root of 2 as a fraction (proof below). However Pythagoras believed in the absoluteness of numbers, and could not accept the existence of irrational numbers. He could not disprove their existence through logic, but his beliefs would not accept the existence of irrational numbers and so he sentenced Hippasus to death by drowning.
The other version of the story is that the guy committed suicide!
The Pythagoreans had built a philosophy based on the "harmony" of ratios of integers, whether they were looking at musical chords or the ratios of the periods of the heavenly bodies. Their motto was "all is number" (referring to positive integers.) The idea that the diagonal of a unit square could not be expressed as such a ratio amounted to an overthrow of both religious and scientific assumptions for them. And the irony is that it was the "Pythagorean theorem" that led to the contradiction.
