was born in the Netherlands in 1959, and has a PhD in space flight dynamics from the Delft University of Technology. Since 1989 he lives in Darmstadt, Germany, where he works for the European Space Agency.
In 1994 he first became aware of the existence of the Voynich MS, and after seeing an illustration of the writing he was immediately attracted to it. After several years of exchanging information about the manuscript with like-minded people, he realised that there was a need for a central repository of facts and theories related to this MS, primarily to guide newcomers. This gradually evolved into one of the best known web resources about the manuscript (http://www.voynich.nu).
Since 2000 he has concentrated mainly on the history of the MS, and he has several publications on this topic. In 2012 he was one of the organisers of a workshop celebrating the 100th anniversary of the re-discovery of the manuscript, in the place where it was found: the Villa Mondragone near Frascati.