Max von Laue
From the Nobel Foundation:
His best known work…for which he received the Nobel Prize for Physics for 1914, was his discovery of the diffraction of X-rays on crystals. This discovery originated, as he related in his Nobel Lecture, when he was discussing problems related to the passage of waves of light through a periodic, crystalline arrangement of particles. The idea then came to him that the much shorter electromagnetic rays, which X-rays were supposed to be, would cause in such a medium some kind of diffraction or interference phenomena and that a crystal would provide such a medium. Although his colleagues Sommerfeld, W. Wien and others, with whom he discussed the idea on a skiing expedition, raised objections to the idea, W. Friedrich, one of Sommerfeld's assistants and P. Knipping tested it out experimentally and, after some failures, succeeded in proving it to be correct. Von Laue worked out the mathematical formulation of it and the discovery was published in 1912. It established the fact that X-rays are electromagnetic in nature and it opened the way to the later work of Sir William and Sir Lawrence Bragg. Subsequently von Laue made other contributions to this subject.
"Max von Laue: Biographical," Nobel Foundation (1914)
Nobel Laureate, Physics Prize, 1914