The heaviest naturally occurring element uranium was discovered and named by German scientist Martin Klaproth in 1789 by purifying pitchblende, a naturally occurring uranium ore. (Note: Uranium was not discovered to be radioactive until we discovered what radioactivity was by observing uranium, in 1896.) He named it after the planet Uranus, which had been discovered in 1781, but was at the time named George.
Wait, what?! Let’s back up a few links. The planet Uranus was discovered by William Herschel, a German-born British astronomer. He first reported it as a comet due to its motion, but later that year, Royal Society astronomers concluded after repeated observation that its movement meant it had to be a planet. Uranus had in fact been spotted many times before (definitely in 1690, possibly in 128 BCE!) but had previously always been misclassified as a star.
Given naming rights to the first new planet discovered in history, Herschel decided history should remember that this scientific achievement occurred in the reign of King George III (yes, the American Revolution guy). This understandably did not go over well with astronomers from other countries, who generally refused to call it George. Some of the other names in use at the time included Herschel, Neptune, and Astraea. Uranus was suggested by German astronomer Johann Elert Bode and ultimately became the consensus choice, owing in part to his colleague Martin’s naming of uranium in 1789. This conflict was not fully settled until British astronomers finally relented and started calling the planet Uranus like everyone else in 1850.
Johann’s proposal of Uranus followed the pattern of the other planets being named after Roman gods. He chose Ouranos, the Greek god of the sky, not realizing that “Uranus” was actually the Latinized form of that name, not the intended Roman god of the sky’s name, Caelus.
Ouranos is probably named for being the rain god, after Proto-Greek ṷorsó-, meaning ”to rain”. This is the same root used in Greek οὐρέω (ouréō), meaning “to urinate”, from which we get the English word urea.
Even in Ancient Greek, Ouranos can’t escape stupid jokes about his name.