American biochemist who received (with Haldan K. Hartline (Hartline, Haldan Keffer) of the United States and Ragnar Granit (Granit, Ragnar Arthur) of Sweden) the Nobel Prize for Physiology or Medicine in 1967 for his work on the chemistry of vision.

While studying in Berlin as a National Research Council fellow (1932–33), Wald discovered that vitamin A is a vital ingredient of the pigments in the retina and, hence, important in maintaining vision. After further research in Heidelberg and at the universities of Zürich and Chicago, he joined the faculty of Harvard University in 1934.

By the early 1950s Wald had succeeded in elucidating the chemical reactions involved in the vision process of the rods (receptors on the retina used for night vision). In the late 1950s, with Paul K. Brown, he identified the pigments in the retina that are sensitive to yellow-green light and red light and in the early 1960s the pigment sensitive to blue light. Wald and Brown also discovered the role of vitamin A in forming the three colour pigments and showed that colour blindness is caused simply by the absence of one of them. Wald became professor emeritus at Harvard in 1977.