Dan Shumow
The Microsoft cryptographer who, six years before Snowden, stood on a stage in Santa Barbara and explained exactly how Dual_EC_DRBG could be backdoored.
At the CRYPTO rump session in August 2007, Shumow and Niels Ferguson gave a short talk on Dual_EC_DRBG, the random number generator NIST had just standardised in SP 800-90. The generator is built on two fixed points, P and Q, on an elliptic curve. Anyone who knows the relationship between them can, after seeing about 32 bytes of output, predict everything the generator produces afterwards. Nobody knew where the points had come from. The talk was carefully worded; in 2013 the Snowden documents showed the suspicion had been right.
Shumow later worked with Marc Stevens on SHA-1 collision detection, a technique that after SHAttered in 2017 was adopted by Git, among others, to spot deliberately crafted collisions.