Aether

The aether was a substance filling background space and thought to be required to explain how light waves could be propagated through space, as all wave transmission requires a medium. Its existence has been postulated a medium for the propagation of electricity, light, and gravitation throughout ages, from the Ancient Greeks, to Newton, to the scientists of the Victorian Era. Aristotle called aether the Fifth Element.

James Clerk 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:

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.