Frank Rowlett
American cryptanalyst who led the team that reconstructed the Japanese PURPLE machine in 1940.
Frank Rowlett led the US Army team that in 1940 rebuilt the Japanese PURPLE machine without having one to examine. The work rested on patterns in the ciphertext, and it gave the Americans readable Japanese diplomatic traffic for much of the war.
Rowlett was one of several people who contributed, but he is the one most often named as the team's leader.