The CAPTCHA security protocol, which distinguishes human users from automated bots online, originated in 1997 through the work of Eilon Solan alongside collaborators Eran Reshef and Gili Raanan. A specialist in game theory and stochastic processes, Solan holds the Dr. Irene Halmos Chair of Game Theory at Tel Aviv University, where he has maintained an active research and teaching career since 2000.
Academic Foundation and Training
Solan completed his undergraduate studies at the Hebrew University of Jerusalem, graduating summa cum laude in mathematics and computer science in 1989. He continued his postgraduate work at Tel Aviv University, where he earned an M.Sc. in mathematics, also summa cum laude, in 1993. His master's thesis on Discounted Stochastic Games was supervised by Ehud Lehrer. In 1998, he received his doctorate from the Hebrew University of Jerusalem under the mentorship of Abraham Neyman, producing a dissertation on stochastic games that earned the Kennedy–Leigh Award for academic excellence.
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Take the IQ test →Contributions to Stochastic and Quitting Games
Much of Solan's research centers on dynamic games, specifically investigating the existence of equilibria in complex environments. He positively resolved the existence of ε-equilibria for three-player absorbing games by refining the vanishing discount factor method. Collaborating with Nicolas Vieille, he introduced the class of quitting games, where players decide at each stage whether to continue or terminate the interaction. They proved the existence of ε-equilibria for these games under specific terminal payoff conditions. Further efforts with Omri and Ron Solan expanded this to general quitting games by applying the martingale central limit theorem and Browder's theorem.
Stopping Games and Mathematical Tools
Solan has analyzed stopping games, a category of dynamic interaction where payoffs are determined by the timing of a player's decision to exit. In partnership with Eran Shmaya, he utilized a stochastic variation of Ramsey's theorem to prove equilibrium existence in discrete-time stopping games. With Rida Laraki, he demonstrated the same for continuous-time games. His work has also produced broader mathematical contributions, including a stochastic generalization of Ramsey's theorem and extensions of Browder's theorem to connected compact Hausdorff spaces. Additionally, he and Vieille developed graph-theoretic methods for measuring the sensitivity of stationary distributions within Markov chains.
Publications and Editorial Service
Solan has authored several key texts in the field, including 'A Course in Stochastic Game Theory' published by Cambridge University Press in 2022 and 'Borel Games' in 2025. He also co-authored the comprehensive textbook 'Game Theory' with Shmuel Zamir and Michael Maschler, which saw a second edition in 2020 and has been translated into Chinese and Hebrew. His editorial contributions include long-term roles at the International Journal of Game Theory, Games and Economic Behavior, and Mathematics of Operations Research. He was elected a Fellow of the Game Theory Society in 2019.
Fast facts
- Born: 1969
- Citizenship: Israel
- Doctoral Advisor: Abraham Neyman
- Current Position: Professor, Tel Aviv University
- Key Invention: CAPTCHA (1997)
- Fellowship: Game Theory Society (2019)
Questions readers ask
What is the focus of Eilon Solan's research?
His research focuses on game theory, particularly stochastic games, stopping games, and stochastic processes.
Did Eilon Solan help develop CAPTCHA?
Yes, he was one of the inventors of CAPTCHA in 1997, working alongside Eran Reshef and Gili Raanan.
Achievements
- Held posts at Tel Aviv University
- Fields: game theory
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