John William Strutt
Profession: Physicist and Nobel Laureate
Why Famous: Discovered argon with William Ramsay, an achievement which earned him the Nobel Prize for Physics in 1904.
Also discovered the phenomenon now called Rayleigh scattering, which can be used to explain why the sky is blue and predicted the existence of the surface waves now known as Rayleigh waves.
Rayleigh's textbook "The Theory of Sound", is still referred to by acoustic engineers today.