Electromagnetism is one of the four fundamental forces. It is responsible for most of what happens in daily life, being responsible for chemistry and indeed the existence of atoms, wherein the quarks that group as protons and neutrons that then group as nuclei electrically attract a pile of electrons.
Electromagnetism manifests as electric fields and magnetic fields. These were thought of as separate until Maxwell set out in 1873 precisely how and why one always implies the other.
Physicists used to assume electromagnetism travelled in a medium they called "ether", because how could you have a wave without a medium. That's just silly. Except it turned out to be the case. The Michelson-Morley experiment established that there was such a thing as a speed of light and that it was apparently constant. This was enough to start Einstein on the path to special relativity.
- Nikola Tesla, once he'd advanced past doing actually useful engineering, was a fount of electromagnetic crankery.
- Dewey Larson's Reciprocal Theory
- Scalar waves should leave you gibbering into the sunset.