Don Coppersmith
IBM cryptographer on the DES team whose 1994 account revealed that the designers knew about differential cryptanalysis in 1974.
Coppersmith worked at IBM and was part of the group that developed DES. In a 1994 paper he explained that the designers had known about differential cryptanalysis since 1974 and had shaped the S-boxes to resist it, a fact kept quiet for two decades. Why it stayed secret has been debated ever since.
He is also known for lattice-based methods for finding small roots of polynomial equations, which have seen wide use in the analysis of RSA.