Why did Max Planck support Einstein’s special theory of relativity?

Max Planck was the first prominent physicist to champion Albert Einstein’s special theory of relativity (1905).12

Planck recognized the theory's profound significance by drawing a parallel between its core principles and his own work in quantum theory. He famously remarked that the velocity of light serves as the absolute core of the theory of relativity, just as the elementary quantum of action is the core of quantum theory.2

By supporting Einstein’s work, Planck helped establish the fundamental theories that revolutionized 20th-century physics, fundamentally altering our understanding of space, time, and atomic processes.3