Willem Dafoe's birth name is William J. Dafoe.
Willem van der Veer's birth name is Wilhelmus Leonardus Joseph Van der Veer.
Wim Hoddes's birth name is Willem Christiaan Hoddes.
Richard Flink's birth name is Richard Martinus Willem Flink.
If you are asking about who played the actor it is William Dafoe but if you are asking about his alter ego it is Norman Osborn
Willem Abel Janszoon is the Dutch explorer's full name.
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The Zeehaen
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Captain Willem Janszoon was the skipper of the Dutch ship Duyfken. A link is provided to the relevant Wikipedia article.
Willem Ward's birth name is Willem Luke Ward.
Willem Mengelberg's birth name is Mengelberg, Josef Willem.
Willem Elzenga's birth name is Willem Lodewijk Elzenga.
Willem Drieling's birth name is Willem Johannes Drieling.
Willem Wilmink's birth name is Willem Andries Wilmink.
Willem van Beusekom's birth name is Willem Jacobus Marius van Beusekom.
Willem Paul Edelman's birth name is Willem Paul Franciscus Xaverius Edelman.