From the Wikipedia page [1]
Karl Widemann or Carl Widemann or Carolus Widemann, was a German author, physician and collector of manuscripts, from Augsburg, and secretary, between 1587 and 1588, of the English alchemist Edward Kelley, at the court of Emperor Rudolph II.
Widemann also worked in Třeboň for the Rožmberks, also known as the Rosenberg family.
Karl Widemann is known for copying and collecting over 30 years the works from Paracelsus. Because of this many unpublished works from Paracelsus survived to the present day. He did the same for the works of Caspar Schwenckfeld, and Widemann's close colleagues Valentin Krautwald and Adam Reusner. After Helisaeus Roeslin's (Helisäus Röslin) death in 1616, his unpublished astrology, theology and kabbalistic work merged into the manuscript collection of Karl Widemann. Adam Haslmayr a close friend of Widemann, wrote him a letter about Rosicrucian people who revealed the Theophrastiam, on December 24th, 1611.
In March 1599 Emperor Rudolph II bought books from Karl Widemann for 500 Taler. However, these books were not catalogued in Rudolph's Kunstkammer inventory.
Mentioned here and here. Voynich Manuscript related article here.