Richard Lenski
Notes
Richard Lenski (born 1956), American evolutionary biologist at Michigan State, who has run the Long-Term Evolution Experiment on twelve populations of E. coli since 1988, now past 75,000 generations. In 2008 one population evolved the ability to metabolise citrate, a novel trait that required several prior mutations to be in place first. It is the cleanest direct observation of evolution by natural selection producing a new capacity, and the frozen samples taken every 500 generations mean the whole history can be replayed.
Wikipedia: https://en.wikipedia.org/wiki/Richard_Lenski