Aether

The aether was a substance which supposedly occupied all of space, and its existence was thought to be required to explain how light waves could be propagated through space, since all wave transmission requires a medium. Its existence has been postulated in various forms ans uses throughout the ages, from the Ancient Greeks, to Newton, to the scientists of the Victorian Era. Aristotle called aether the Fifth Element.

Indeed, James Clark Maxwell, the father of Electromagnetic Theory and a figure widely considered to be one of the greatest scientists to have lived, utilizes aether in his treatise:

--James Clerk Maxwell, A Treatise on Electricity and Magnetism/Part IV/Chapter XX

Aether in Modern Science
It is popularly believed that Einstein abolished the aether in science with his Theory of Relativity. However, the following quotes suggest a different story.