Gotthilf Heinrich Ludwig Hagen (March 3, 1797 - February 3, 1884) was a German physicist and hydraulic engineer.

Hagen was born in Königsberg, Brandenburg-Prussia (today Kaliningrad, Russia).

Independentlly of Jean Louis Marie Poiseuille (1797-1869) Hagen in 1839 carried out the first carefully documented friction experiments in low-speed tube laminar flow, from which the Hagen-Poiseuille law has arised.