From what I remember, Einstein had a hard time believing that light can travel in the empty space. Therefore, it was thought that their was an invisible material, without any mass, without any smell, without anything, that would allow light to travel through it.
Since then, many experiments were made to discover that ether, without success. The unsuccessful attempts to detect ether could be explain with some god d*** theory that was as complicated as it was ridiculous. Therefore, after a while, scientist decide to apply a simple procedure which says that if you have two theories that can explain the same thing, the simplest one is the most probable. Since then, the idea of ether has been dropped.
I hope I did not make any mistakes. This is what I rememebr from some class in University.
Cheers