Paracelsus (/ˌpærəˈsɛlsəs/; born Philippus Aureolus Theophrastus Bombastus von Hohenheim, 11 November or 17 December 1493 – 24 September 1541) was a Swiss German Renaissance physician, botanist, alchemist, astrologer, and general occultist. He founded the discipline of toxicology. He is also known as a revolutionary for insisting upon using observations of nature, rather than looking to ancient texts, in open and radical defiance of medical practice of his day.