Jacques Patarin
French cryptographer who first broke Matsumoto–Imai and then invented the multivariate schemes – HFE and Oil and Vinegar – the field still builds on.
In 1995 Patarin showed that the Matsumoto–Imai scheme leaked linear relations between plaintext and ciphertext, enough to solve for the message. His answer was to design his own: Hidden Field Equations (HFE, 1996) hides a polynomial over an extension field, and Oil and Vinegar (1997) splits the variables into two kinds, mixed in a way only the key holder can untangle.
The balanced version of Oil and Vinegar fell to Aviad Kipnis and Adi Shamir in 1998, so in 1999 Patarin, Kipnis and Louis Goubin presented Unbalanced Oil and Vinegar – UOV – which still stands. SFLASH, a signature scheme he co-designed, was selected by the EU's NESSIE project in 2003 and broken in 2007. That is roughly the rhythm the field lives by.