Henri Poincaré  (1854 -1912) French mathematician and physicist. A genius by definition. Although dated in spirit by now, his more popular books on science are (or should be) required reading in any comprehensive physical science program. He was a walking contradiction of classical method and groundbreaking modeling. We have still to catch up with him in many ways.

One of his key concepts was that science can only
deal with relations among things, rather than with things in themselves. Young Einstein was inspired by this fascinating concept. In 1905 both Poincaré and Einstein published papers which defined special relativity. But Poincaré focused only on the electron.
Einstein left his equivalent formulations open to all matter. Poincaré remained silent on this difference and praised Einstein only for his work on the quantum concept of light. Paradoxically, Einstein never quite accepted the inherent uncertainties and complexities of quantum mechanics.

One of Poincaré's greatest discoveries was to note that we cannot conclude that a system such as the solar system is stable. With this he inaugurated the area of complexity studies but it would take a century for this field of science to bloom.