Beldak was an individual known in the 23rd century for working with and writing about the principles of physics.
An Excalbian who took the form of Emilie du Chatelet told Doctor McCoy that she was interested in the principles of physics, and learned more about it from the works of such individuals as Beldak, Newton, Leibnitz, Einstein, and de Varlane. (TOS novel: Savage Trade)