Siegfried Woldhek studied theoretical ecology in Amsterdam and then worked for the Dutch Society for the Protection of Birds, first as biologist and later as CEO (1985–1990). From 1990–1998 he was CEO of World Wildlife Fund-Netherlands and until 2002 he was in charge of the Action Network for WWF-International. During the next ten years he founded and led NABUUR.COM. HRH Prince Bernhard awarded him the Order of the Golden Ark for his contribution to conservation.
Woldhek has made literary and political portraits for leading Dutch newspapers since 1976. His work is often exhibited and has been featured in dozens of books, including seven books dedicated to his portraits. More than 2000 portraits can be found on his website, making it one of the largest collections of portraits of the entire Internet. Several Dutch museums have acquired his work, as did the Metropolitan Museum in New York which has exhibited these in the exhibition Infinite Jest: Caricature and Satire from Leonardo to Levine.
Siegfried Woldhek was a TED speaker. His talk about the face of Leonardo da Vinci has been viewed well over a million times. For his contribution to Dutch literature he was awarded the GH's Gravesande prize. He received the prize for the best Dutch political cartoon in 2011.