Aelius Galenus or Claudius Galenus (; ; September 129 AD – /), better known as Galen of Pergamon , was a prominent Greek physician, surgeon and philosopher in the Roman empire. Arguably the most accomplished of all medical researchers of antiquity, Galen influenced the development of various scientific disciplines, including anatomy, physiology, pathology, pharmacology, and  neurology, as well as philosophy and logic.

OpenGALEN is a not-for-profit organisation that provides an open source medical terminology. This terminology is written in a formal language called GRAIL (GALEN Representation And Integration Language) and also distributed in OWL.