Ernst Walter Mayr (5 July 1904, Kempten, Germany – 3 February 2005, Bedford, Massachusetts), was a German American scientist. He was one of the 20th century's leading evolutionary biologists. He was also a well-known taxonomist, tropical explorer, ornithologist, historian of science, and naturalist. He was a leading contributor to the modern evolutionary synthesis. He was especially interested in how new species formed.