Erich Otto Ernst Rieger (born 1935 in Würzburg, Germany) is a German astrophysicist who spent his research career at the Max Planck Institute for Extraterrestrial Physics (MPE) near Munich. He is notable for his 1984 discovery of the period of ~154 days in solar flares. Since the discovery, the period has been confirmed in most heliophysics data in the Solar System, including the interplanetary magnetic field, and has become known as the Rieger period (PR).