The man in the picture is Max Planck

In physics, the Planck length, denoted ℓP, is a unit of length, equal to 1.616229(38)×10−35 metres. It is a base unit in the system of Planck units, developed by physicist Max Planck. The Planck length can be defined from three fundamental physical constants: the speed of light in a vacuum, the Planck constant, and the gravitational constant.
The Planck length is about 10−20 times the diameter of a proton. It can be defined using the radius of the hypothesized Planck particle.
(wikipedia