Benzer was best known for his detailed mapping of the rII locus in bacteriophage. Benzer was able to resolve mutants that were likely to be only a single nucleotide apart. His work on mapping deletions led directly to the conclusion that the genetic codon should consist of three nucleotides. In honor of Seymour Benzer, John Dennehy has selected his 1955 paper as this week's citation classic [Benzer, S. (1955)].
You can read about Benzer's famous experiments in the article he wrote for Phage and the Origins of Molecular Biology: Adventures in the rII region.
Later on in his career, Benzer worked with Drosophila melanogaster studying behavioral mutations, including some that affect the circadian rhythm. Since this is Coturnix's field, he has posted his own tribute to Benzer [In Memoriam: Seymour Benzer].
Other notable tributes:
Carl Zimmer [Farewell, Seymour Benzer].
PZ Myers [We've lost a great one: Seymour Benzer].
It's sad to note that most younger scientists, and almost all undergraduates, have never heard of Seymour Benzer. Mostly this is sad because it makes me realize how old I am!
[Photo Credit: The photo shows Francis Crick (left) speaking to Seymour Benzer in 1964 (The Francis Crick Papers)]