Which physicist supervised Albert Einstein's doctoral thesis?

Alfred Kleiner supervised Albert Einstein’s doctoral work at the University of Zurich. Kleiner was a Swiss physicist and professor of experimental physics who became Einstein’s doctoral adviser and one of the examiners of his dissertation.

Einstein’s successful doctoral thesis was submitted in 1905 and concerned a method for determining molecular dimensions. Kleiner initially found Einstein’s early dissertation proposal unsuitable, and Einstein eventually pursued a more conventional problem involving solutions, viscosity, diffusion, and the size of molecules. The work was accepted after Einstein revised it.

Kleiner is often overshadowed by the famous names associated with Einstein’s later career, such as Max Planck, Hendrik Lorentz, and Hermann Minkowski. Those physicists influenced or interacted with Einstein, but they did not supervise his doctorate. Einstein received the University of Zurich doctorate in 1906, based on the dissertation completed during his remarkable 1905 annus mirabilis.