Johann Weyer, Dutch physician (d. 1588)
Johann Weyer or Johannes Wier (Latin: Ioannes Wierus or Piscinarius; 1515 – 24 February 1588) was a Dutch physician, occultist and demonologist, disciple and follower of Heinrich Cornelius Agrippa.

He was among the first to publish against the persecution of witches. His most influential work is De Praestigiis Daemonum et Incantationibus ac Venificiis ('On the Illusions of the Demons and on Spells and Poisons'; 1563).