Stathis K. Zachos (Greek: Στάθης (Ευστάθιος) Ζάχος; born 1947 in Athens) is a mathematician, logician and theoretical computer scientist.
Zachos received his PhD from the ETHZ (Swiss Federal Institute of Technology Zurich) in mathematics (and computer science), 1978.
[5][6][7] One of his important contributions, using interactive proof systems and probabilistic quantifiers, is that the graph isomorphism problem is not likely to be NP-complete (joint with R. Boppana, J.
[8] Graph isomorphism is one of the very few celebrated problems in NP that have not been shown yet to be either NP-Complete or in P. Zachos's most influential work was introducing and proving properties of the class Parity-P (with Christos Papadimitriou).
He has co-organized International Conferences: STOC '87 (and programming committee of STOC '01), ICALP, CiE (Computability in Europe), PLS, ASL (Association for Symbolic Logic) European Summer Meeting, ACAC (Athens Colloquium on Algorithms and Complexity) and NYCAC (New York Colloquium on Algorithms and Complexity).