The discovery of three types of cones in the retina is attributed to the German physiologist and anatomist Ewald Hering, who is known for his work on color vision. In the late 19th century, Herring proposed that color vision relied on three types of receptors in the eye, each sensitive to a different range of wavelengths of light. He believed that these receptors corresponded to the three primary colors of light: red, green, and blue. Hering's theory of color vision was later refined and expanded upon by other scientists, including the American physiologist H. E. Ives and the English physicist James Clerk Maxwell. Today, we know that there are three types of cones in the retina that are responsible for color vision, and this is commonly referred to as the trichromatic theory of color vision.