This type of Mercury doesn’t go into retrograde, but it was associated with the Swift Planet (a nickname for the planet Mercury) by alchemists trying to transform the element and other metals into gold. (Spoiler: It didn’t work.)
Mercury was among one of the first metals known by humankind, with its chemical symbol (Hg) coming from the Greek word hydrargyrum—meaning liquid silver or quicksilver. It perfectly describes mercury’s shiny, liquid properties—the only metal on earth that is liquid at room temperature. Alchemists and early scientists were drawn to mercury's ability to flow like water, but behave like a metal.
Alchemists believed mercury was the "First Matter," the substance from which all metals were created. They thought you could change, or transmute, mercury into gold. They obviously weren’t successful, but their experiments laid the foundation for modern chemistry! These experiments led to the development of distillation and sublimation, techniques still used in research today.
The unique metal was highly prized by ancient cultures, believing it to have healing powers and grant immortality. China’s first emperor, Qin Shi Huang, drank a potion of mercury and powdered jade seeking to live forever; he promptly died. Despite mercury’s toxicity, the element would continue to be used in medicine for centuries, even being used to treat syphilis as recently as the 1950s.
Beyond medicine, mercury was the key to unlocking basic science. It was key to developing barometers (which measure air pressure) and blood pressure cuffs because it reacts consistently to pressure changes. Mercury was also perfect for thermometers because it expands and shrinks predictably with temperature. Today, we use safer materials for most of these tools, but mercury is still used for more advanced things, like electrodes, coulometers (a way to measure chemical reactions), and high-powered microscopes.