Adolf Karl Ludwig Claus (June 6, 1838, in Kassel; May 4, 1900, in Horheim) was a German chemist who was the first to propose a hexagonal structure for benzene. His parents were the mint master Heinrich Claus and Charlotte, née Richter. His brother was the zoologist Carl Friedrich Claus (1835-1899). Claus attended the gymnasium in his hometown of Kassel and initially studied medicine at the University of Marburg. In 1859, he became a member of the Corps Teutonia Marburg. However, he switched to chemistry as a student of Hermann Kolbe. He earned his doctorate under Friedrich Wöhler. In 1867, he became an associate professor and in 1876 a full professor of chemistry and technology at the University of Freiburg im Breisgau, where he served as dean in 1881/82. Claus conducted research in the field of heterocycles, primarily on quinoline derivatives, as well as condensed ring systems such as naphthalene, anthracene, and phenanthrene. During the contemporary debate on the structure of benzene, he was the first to use a hexagonal structure for the molecule.