Largest-ever SPAC will return $4 billion to investors after failing to complete a deal.

Two years after raising the largest-ever special purpose acquisition company, or SPAC, the billionaire Bill Ackman has concluded that he will be unable to do a deal that meets its needs.

In a

, Mr. Ackman said he would return the funds of his $4 billion SPAC, Pershing Square Tontine Holdings, because it was “unable to consummate a transaction that both meets our investment criteria and is executable.”

SPACs,…