**Alexander** (**Alekos**) **Sotirios Kechris** (Greek: Αλέξανδρος (Αλέκος) Σωτήριος Κεχρής; born March 23, 1946) is a set theorist and logician at California Institute of Technology.

He has made major contributions to the theory of Borel equivalence relations and the theory of automorphism groups of uncountable structures. His research interests cover foundations of mathematics, mathematical logic and set theory and their interactions with analysis and dynamical systems.

Kechris earned his Ph.D. in 1972 under the direction of Yiannis N. Moschovakis, with a dissertation titled *Projective Ordinals and Countable Analytic Sets*. During his academic career he advised 23 PhD and sponsored 20 postdoc students.

In 2012 he became an Inaugural Fellow of the American Mathematical Society.

1986 - Invited Speaker at the International Congress of Mathematicians in Berkeley (Mathematical Logic & Foundations)
1998 - a Gödel lecturer (Current Trends in Descriptive Set Theory).
2003 - received along with Gregory Hjorth the Karp Prize for joint work on Borel equivalence relations, in particular for their results on turbulence and countable Borel equivalence relations
2004 - Tarski Lecturer (*New Connections Between Logic, Ramsey Theory and Topological Dynamics*)
A. S. Kechris, "Classical Descriptive Set Theory", Springer-Verlag, 1995.
H. Becker, A. S. Kechris, "The descriptive set theory of Polish group actions" (London Mathematical Society Lecture Note Series), University of Cambridge, 1996.
A.S. Kechris, V.G. Pestov and S. Todorcevic, "Fraïssé limits, Ramsey theory and topological dynamics of automorphism groups", Geometric and Functional Analysis 15 (1) (2005), 106-189.
A.S. Kechris, "Global Aspects of Ergodic Group Actions", Mathematical Surveys and Monographs, 160, American Mathematical Society, 2010.