Given her legendary status today, it’s incredible to think that Katharine Hepburn was once considered something of a box office flop. A string of poorly received movies had left her in something of a slump by the late 1930s, and so, disillusioned by Hollywood and licking her wounds, she returned home to New York. There, she accepted a role in a new Broadway play written just for her: The Philadelphia Story.

The play was an instant success, and Hepburn—who had astutely eschewed a salary upfront and instead negotiated an impressive 10% of the box office receipts—made a fortune from it. Not only that, but the huge success brought her back to the attention of Hollywood’s most powerful movie moguls and in 1940 she returned to the silver screen in the movie adaption of The Philadelphia Story; to some of the most rave reviews of her career.

As the play had been written especially for her, Hepburn was given considerable creative control over the movie too, and the role she played—Tracy Lord, a fiercely strong, sharp-minded, and independent young woman—set the template for many of Hepburn’s most quintessential performances. The Philadelphia Story was very much Hepburn’s movie—but according to the movie billing, you’d be forgiven for thinking otherwise.

When it came to casting The Philadelphia Story, Hepburn’s first choice of co-stars were Clark Gable and Spencer Tracy. Unfortunately, scheduling conflicts meant neither were available, and her supporting roles eventually fell to James Stewart and Cary Grant. Yet despite Hepburn’s character being the protagonist—and despite Stewart’s character having more dialogue—Grant demanded that he would only accept the part if he received the movie’s top billing. Incredibly, his demands were met, and The Philadelphia Story was marketed with Grant’s name first.

Why was Grant so adamant that his name be listed first? Some critics saw this as little more than a Hollywood power play—an instance of one of the movie industry’s hottest A-listers merely asserting his box office supremacy. But it seems likely that his demand was a more charitable one: Grant’s top billing came with an inflated salary of $137,500 (equivalent to $2.5 million today) and as soon as he signed his contract, he donated his entire paycheck to the British War Relief effort.