Carl Friedrich Wilhelm Claus (1835 – 1899) was a German zoologist. He was an opponent of the ideas of Ernst Haeckel.
Claus studied at the University of Marburg and the University of Gießen with Rudolf Leuckart. He worked at the university of Würzburg. In 1863, he became professor of zoology at Marburg, in 1870 at Göttingen and in 1873 at Vienna.He was head of the oceanographic research station in Trieste and was specialized on marine zoology and there his interest was focused on crustaceans. During his research on cell biology he coined the word phagocyte.
In nineteenth century, there were many alkali manufacturing plants in England producing sodium carbonate (Na2CO3) by the Leblanc process. The original Claus process was developed by Carl Friedrich Claus, a chemist working in England, for the purpose of recovering sulfur from the waste calcium sulfide (CaS) generated by the Leblanc process. As a catalyst, he chose a bog iron ore and later bauxite (a mineral with a high alumina content).In 1883, Claus was granted a British patent for the process.