Johann Isaac Hollandus

Isaac and Johann Isaac Hollandus were a 17th-century pseudonymous Dutch alchemist duo. It is not clear if they were father-and-son, brothers, or even the same person.

They were originally believed to be from the 14th or 15th century, predating Paracelsus. They were among the most famous alchemists in Europe at one point in time. Johann von Löwenstern-Kunckel stated that "the incomparable Isaac Hollandus" "had more knowledge in his little finger than Van Helmont in his whole body". However, Isaac and Johann Isaac Hollandus fell out of favor in the early 20th century after it was concluded they were actually post-Paracelsus.