Michael Faraday - formulated the principle behind electromagnetic induction. Faraday is credited with his discovery of induction in 1831, and further on, Maxwell has described Faraday's discovery mathematically as the Faraday's law of induction.James Clerk Maxwell - contributed in developing equations that showed the relationship of electricity and magnetism. He predicted the existence of electromagnetic spectrums and he described them as light that is a propagating wave of electric and magnetic fields. He later on published the mathematical theory of electromagnetic fields and created a new era of physics where he unified magnetism, electricity, and light.
Hans Christian Oersted - showed how a current carrying wire behaves like a magnet. Hans Oersted was the first person who have noticed the deflection of the needle in the compass whenever a current was passed through the wire. Joseph Henry- was an American scientist and engineer. While building electromagnets, he discovered the electromagnetic phenomenon of self-inductance. He also discovered mutual inductance, independently of Michael Faraday, but Faraday was the first to publish his results.
Thanks! This info is such a great help to understand electromagnetic wave theory!