There’s something disarming about Philippe Selendy, the soft-spoken, 49-year-old litigation whiz who helped the Federal Housing Finance Agency wrestle $20 billion from banks accused of selling shoddy mortgage-backed securities to Fannie Mae and Freddie Mac. Maybe it’s his earnest, academic style, or his youthful looks.

But his colleagues at Quinn Emanuel Urquhart & Sullivan know what his adversaries eventually find out: When it comes to litigation, Selendy is an archangel of defeat. His opponents in the FHFA cases—18 financial institutions that included Bank of America Corp., JPMorgan Chase & Co. and UBS Americas Inc.—banked on early dismissals. Instead they faced setback after setback: The FHFA won critical discovery on the massive number of loans at issue, and the courts repeatedly rejected the banks’ core arguments that the FHFA lacked standing and had missed its deadline to sue.