The all-too-common phrase "the butler did it" is commonly attributed to Mary Roberts Rinehart (1876-1958). Mary was a very popular writer who authored over 50 books, many of which became best-sellers. Known as "the American Agatha Christie," Mary (also a playwright) at one point had three plays running simultaneously on Broadway.
Mary was the first writer to use the "once naive but now older and wiser woman narrating the story" device in her novels. She also created a super-criminal called The Bat (1920), who was cited by Bob Kane as one of his inspirations for Batman. Mary's first book The Circular Stairs was published in 1908.
In 1930, Mary's book The Door was published and (spoiler alert) in the story the butler does, indeed, do it. Although Mary Roberts Rinehart is generally credited with the origin of the expression, the words "the butler did it" do not actually appear in the book. Mary was to use the "butler as criminal" device in other novels during her illustrious writing career.
Before Mary Roberts Rinehart it was extremely rare for a butler to be the bad guy in any work of fiction. Sir Arthur Conan Doyle did use the device in an 1893 detective story called "The Musgrave Ritual" from The Memoirs of Sherlock Holmes. Though not the actual central bad guy, the butler in this tale is found dead beside the Musgrave family treasure. "The butler, guilty of betrayal and theft, paid with his life for his perfidy." -as The Oxford Companion to Crime and Mystery Writings puts it.
Also, in Agatha Christie's The Murder of Roger Ackroyd (1926) suspicion initially falls on Ackroyd's butler, Parker, because of his criminal past.
Before Mary Roberts Rinehart, it was actually looked down upon in some circles to make the butler the criminal or the heavy in fiction. In his 1928 essay "Twenty Rules for Writing Detective Stories," S.S. Van Dine spells it out plainly in rule eleven: "A servant must not be chosen by the author as the culprit." He continues, "This is begging a noble question. It is a too easy solution. The culprit must be a decidedly worth-while person -one that wouldn't ordinarily come under suspicion."
Only one other known detective novel prior to Mary Roberts Rinehart's has the butler committing the key, pivotal crime. The Strange Case of Mr. Challoner by British novelist Herbert George Jenkins (1921) tells the tale of a criminal butler.
Although not actually the first, it was Mary Roberts Rinehart who made "the butler did it" a common device in detective novels. Soon thereafter, the bit became so popular it was considered a cliche and spawned many satirical jabs.
In 1933, Damon Runyon published the satirical story "What, No Butler?" and in 1957 P.G. Wodehouse put out a novel sarcastically titled The Butler Did It. Mary's novel The Door was also adapted into a musical called The Butler Did It, Singing.
Besides being a highly successful novelist and playwright, Mary Roberts Rinehart lived a full and fascinating life. During World War I, she became the first female war correspondent in Belgium. In 1929, she helped two of her sons found the publishing house of Farrar & Rinehart. Now the family name survives as Holt, Rinehart, & Winston.
For many years Mary was a regular contributor to the Saturday Evening Post. Her writings were extremely popular and helped shape middle-class values, manners, and conventions.
In the mid-1940s Mary developed breast cancer, which led to a radical mastectomy. She went public with her story (such occurrences were usually unspoken of in public at the time). Mary's interview ("I Had Cancer") was published in a 1947 article in the Ladies Home Journal. The article encouraged woman to have breast exams.
Mary Roberts Rinehart died at the age of 82 in her Park Avenue home in New York City.