Alexey Poyarkov, a former gold-medal winner of the International Mathematical Olympiad for high-school students, spent most of his early career honing algorithms at technology companies such as Microsoft Corp., where he helped make the Bing search engine smarter at ferreting out pornography.

Last year, a bidding war for Mr. Poyarkov broke out among hedge-fund heavyweights Renaissance Technologies LLC, Citadel LLC and TGS Management Co. When it was over, he went to work at TGS in Irvine, Calif., and could earn as much as...