Shai Halevi
Israeli-American cryptographer who made fully homomorphic encryption actually run and showed where the random oracle model breaks.
In 1998, with Ran Canetti and Oded Goldreich, Halevi showed that some schemes are secure in the random oracle model yet insecure with every real hash function. The counterexample is contrived, but it has made people read every proof in that model with a certain asterisk ever since.
At IBM Research in 2011 he and Craig Gentry produced the first working implementation of Gentry's fully homomorphic scheme. A single operation took minutes and the keys ran to gigabytes, but it worked. Two years later came HElib, written with Victor Shoup, which became the reference for practical homomorphic encryption. Halevi also designed the wide-block modes CMC and EME with Phillip Rogaway for disk encryption.