James Clerk Maxwell opened the doors of science farther than anyone ever had or possibly ever will. One of his most famous accomplishments was the derivation of equations linking electricity and magnetism ("Maxwell's Equations"), which eventually led to the development of quantum physics in the early 1900's and to Einstein's general theory of relativity. His discoveries were the single most important bit of knowledge mankind could ever have.
The four partial deferential equations he formulated were extensions of Faraday's theories of electricity and magnetic lines of force. Maxwell showed through mathematics that an oscillating electric charge produces an electromagnetic field which propagate at the speed of light. He also postulated that visible light is only a small part of the spectrum of frequencies that electromagnetic energy can have.
He is also responsible in part for the first color photograph. He discovered the process while studying color blindness. He did it by taking three separate images using a red, a blue and a green filter then recombining or adding them back together. This process was called the "trichromatic process" and was the basis for modern color photography.
Note: There seems to be some discrpancy as to Mr. Maxwell's middle name. Numerous sites have it as being "James Clerk Maxwell" while other sites have it as being "James Clark Maxwell". Using google smackdown the phrase "james clerk maxwell" gets 17,200 hits, while "james clark maxwell" gets 1,060.More Info