Who was the first media spoiler?

My guess is that the phrase "spoil the story," which dates back as far as 1926, morphed into the contemporary term "spoiler."

Before we became saturated by a media landscape that threatens to subvert every element of surprise, people probably didn't need a single go-to word for "ruining the ending." Without VCRs, television spoilers were less likely to be a problem before the 1970's. And in the rare instances of movie spoilers, people were probably content to describe it as "ruining the ending" or "spoiling the story."

To tell you would be to ruin the story, and to ruin the ending would be sacriligious

• from Gems of the Vieux Carre: The Story of Four Historical Romances of the French Quarter of Old New Orleans, Depicting Living Conditions and Home Life of the Creole and Their Slaves in Pre-Civil War Days by Pierre Paul Ebeyer, 1945.

Ngram shows some earlier use of the phrase "Spoil the ending." However, the earliest quote I can find on google is actually about Dickens's revision to the ending of *Great Expectations:

The dominant feeling about Dickens's revision can perhaps be summed up by George H. Ford's statement that Dickens "accepted Bulwer- Lytton's advice to spoil the ending of Great Expectations."

• From Thoth by Graduate students of the English Dept. of Syracuse University, 1970

Interestingly, Ngram shows "spoil the story" much more frequently than "spoil the ending," "ruin the ending," or "ruin the story."

"Spoil the story" appears as far back as this 1926 edition of Overland Monthly and the Out West Magazine.

In the meantime the ever vigilant eye of Scotland Yard has been taking impressions from the beginning . . . but we do not wish to spoil the story. You will be thrillingly entertained from the first to the last page.

Now the remaining question is when did the act of "spoiling the story" become a "spoiler?"

The first use of "plot-spoiler", with reference to spoiling movie plots, appeared at least as early as 1920, in film's silent era:

"I just love the big organ at Ye Liberty," says Helen Chunx, "for when it plays I can't hear a word of what the plot-spoiler back of me has to say. But when the organ is temporarily incapacitated, I suffer intensely, because the piano is not strong enough to drown the voice of that poor fish which insists on telling the story of the picture in advance. But I beat him to it, one time. I put chewing-gum in my ears."

The Honolulu Advertiser, 25 Jul 1920, Page 4 (paywalled link).

Use of 'spoiler' in the popular press with that specific reference and sense recurs with increasing frequency through the 1930s, 40s, 50s, and 60s.