The story
Derived in 1883 by French electrical engineer Léon Charles Thévenin; however, it had been independently derived in 1853 by German physicist Hermann von Helmholtz.
Etymology from Wiktionary, CC BY-SA 4.0.
Thévenin's theorem
Today it means: A theorem which states that any electric circuit between two terminals containing only resistors, voltage sources, and current sources can be equivalently replaced with a single voltage source and resistor. Full definition →