Bill Ackman has endured a humbling three years: big public losses, an exodus by investors, and what a chief executive calls an “ass-whooping” in an activist campaign. Now, the hedge fund titan could be making a comeback.

Ackman’s publicly-traded investment vehicle, Pershing Square Holdings, has gained more than 20% from a March low, based on its net asset value. Through July 10, the closed-end fund was up 10.4% on the year — about double the return on the S&P 500 index.