Whose principle explains why a wave bends around obstacles and spreads out through openings?

Christiaan Huygens, a Dutch scientist of the 17th century, proposed this wave model of light and other waves. His principle helps explain diffraction, reflection, refraction, and the way waves propagate. By imagining every point on a wavefront as producing tiny secondary waves, the next wavefront can be constructed geometrically. The idea was crucial in the development of wave optics.