Max Planck

In 1900, trying to make the mathematics of glowing hot bodies come out right, Planck assumed that energy comes in discrete packets. He called it an act of desperation and spent years hoping it would prove unnecessary; instead it began quantum physics.

His life outside the work was a series of losses: one son killed at Verdun, both daughters dead in childbirth, his house destroyed by bombing, and a second son executed in 1945 for his part in the plot against Hitler. His gravestone gives his name and the value of his constant.