It's not accurate to say one person "discovered" electromagnetism. It's a complex phenomenon that was understood through the contributions of many scientists over time. Here's a breakdown:

* Hans Christian Ørsted (1820): He was the first to demonstrate a connection between electricity and magnetism, showing that a compass needle deflected when placed near a wire carrying an electric current.

* André-Marie Ampère (1820-1827): Ampère built upon Ørsted's discovery and developed mathematical laws to describe the forces between electric currents and magnets. He is considered the "father of electromagnetism."

* Michael Faraday (1831): He demonstrated electromagnetic induction, the principle behind generators and transformers, showing that changing magnetic fields can produce electric currents.

* James Clerk Maxwell (1861-1865): Maxwell unified the existing knowledge of electricity, magnetism, and light into a comprehensive set of equations, showing that light is an electromagnetic wave.

So, while Ørsted's discovery was a pivotal moment, understanding electromagnetism required the combined efforts of many brilliant minds.