Kamal Nahas in The Scientist:
Peter Hegemann, a biophysicist at Humboldt University, has spent his career exploring interactions between proteins and light. Specifically, he studies how photoreceptors detect and respond to light, focusing largely on rhodopsins, a family of membrane photoreceptors in animals, plants, fungi, protists, and prokaryotes.1 Early in his career, his curiosity led him to an unknown rhodopsin in green algae that later proved to have useful applications in neuroscience research. Hegemann became a pioneer in the field of optogenetics, which revolutionized the ways in which scientists draw causal links between neuronal activity and behavior.
In the early 1980s during his graduate studies at the Max Planck Institute of Biochemistry, Hegemann spent his days exploring rhodopsins in bacteria and archaea. However, the field was crowded, and he was eager to study a rhodopsin that scientists knew nothing about. Around this time, Kenneth Foster, a biophysicist at Syracuse University, was investigating whether the green algae Chlamydomonas, a photosynthetic unicellular eukaryote related to plants, used a rhodopsin in its eyespot organelle to detect light and trigger the algae to swim. He struggled to pinpoint the protein itself, so he took a roundabout approach and started interfering with nearby molecules that interact with rhodopsins.2
More here.