In 1995, Köhler received a doctorate in natural sciences at the Goethe University Frankfurt with his thesis on the systematics and ecology of black iguanas (genus Ctenosaura).
The projects of Köhler and his research group focus on the study of neotropical herpetofauna in Central and South America, in particular in Mexico, Costa Rica, Panama, Nicaragua and Bolivia.
Since April 1998, Köhler led a breeding program in collaboration with the Frankfurt Zoological Society in Utila.
[3][4] Köhler was involved in the original descriptions of more than 120 species of reptiles and amphibians in many genera, including Agama, Anolis, Brookesia, Ctenosaura, Paracontias, Stenocercus, Leptopelis and Pristimantis.
[7] In 1992, Köhler's wife Elke founded the Herpeton Verlag, a special interest publishing house in Offenbach with the aim of providing reptile owners with particularly well-founded knowledge about their wards.