Apart from royalty, this name was only moderately popular in France during the Middle Ages. After the French Revolution, when Louis XVI was guillotined, it became less common.
The Normans brought the name to England, where it was usually spelled Lewis, though the spelling Louis has been more common in America. Famous bearers include French scientist Louis Pasteur (1822-1895), French actor Louis de Funès (1914-1983), Scottish author Robert Louis Stevenson (1850-1894), who wrote Treasure Island and Dr Jekyll and Mr Hyde, and American jazz musician Louis Armstrong (1901-1971).
There was a medieval English form of this name, Helewis, though it died out after the 13th century. In the 19th century it was revived in the English-speaking world in the form Eloise.