Before Professor Plum, Miss Scarlett and Colonel Mustard gathered on a game board to claim their first victim—wielding a revolver, a rope or a lead pipe—a British musician named Anthony Pratt was watching murder-mystery scenarios unfold in European country mansions, where he played piano. Long before that game board became a global multi-million-seller and was inducted into the Toy Hall of Fame, Pratt was taking mental notes as guests in these elegant homes play-acted dastardly crimes involving skulking, shrieking and falling “dead” to the floor.

Years later, during World War II, Pratt recreated those murder-mystery parlor games in miniature, as a board game called Murder! (later Clue). The longtime Birmingham resident, who worked in a local munitions factory during the war, invented the suspects and weapons between 1943 and 1945, as a way to pass the long nights stuck indoors during air-raid blackouts. His wife, Elva, assisted, designing the game board on their dining-room table.

By that time, Pratt had become something of a crime aficionado. In a 2009 interview, his daughter Marcia Davies said her father was an avid reader of murder fiction by Raymond Chandler and others. (Certainly his game carried strong echoes of novels like Agatha Christie’s 1942 The Body In The Library, in which the staid Colonel and Mrs. Bantry of “Gossington Hall” are informed by their maid of a comely blonde corpse in their dusty library.)“He was fascinated by the criminal mind,” Davies said of her father. “When I was little he was forever pointing out sites of famous murders to me.”

In 1947, Pratt patented the game and sold it to a U.K.-based game manufacturer named Waddington’s and its American counterpart, Parker Brothers (now owned by Hasbro). But because of post-war shortages the game was not released until 1949—as Cluedo in England and Clue in the United States. In both versions, the object is for players to collect clues to figure out the murder suspect, weapon and location. The game took place in a Victorian mansion. The victim’s name? Mr. Boddy.

Although the idea behind Clue hasn’t changed over the years, the board game has undergone countless updates.

Pratt’s original patent, which included 10 characters and additional weapons such as the shillelagh (an Irish walking stick) and hypodermic syringe, was streamlined for efficiency; in the released version of Clue, only six characters and six weapons remained. Of those weapons, the rope token has since been updated from an actual piece of string to a plastic facsimile. And the lead pipe token, made from a piece of actual (poisonous) lead in the original version of Clue, was updated to steel in 1965, then to pewter. A baseball bat and gun with silencer have since been added.

Characters have evolved through the decades to keep up with fashion, hairstyles and pop-culture trends. “The first (1949) version would look very old-fashioned now,” says Nicolas Ricketts, curator of table games at the Strong Museum of Play in Rochester, New York. Versions sold in the 1960s had animated-looking characters, mirroring the growing popularity of Saturday morning cartoons, and the 1980s versions adopted the slick style of the decade.

In 2008, suspects received updated 21st-century identities; among them, Colonel Mustard the military man became Jack Mustard the soccer star, and Professor Plum the archaeologist became Victor Plum, a smartypants billionaire video-game-designer. The mansion, meanwhile, got a spa and home theater.

One of the most significant changes to Clue in the last 70 years, says Ricketts, came with the introduction of a rare new character. In 2016, Hasbro’s Clue killed off the housekeeper Mrs. White, replacing her with the more accomplished Dr. Orchid, the adopted daughter of the mansion’s owner. Dr. Orchid has a fancier career—she’s a working scientist with a Ph.D.—but she comes with a sinister background, having been expelled from her Swiss boarding school after a (dun dun dun!) near-fatal daffodil-poisoning incident.

In addition to inspiring a 1985 film, a touring musical, and a handful of game shows, Clue has spawned dozens of international editions and numerous pop-culture spinoff versions. Film-related riffs include a Star Wars Clue, with a three-dimensional game board, and an Alfred Hitchcock version that allows players to assume the roles of characters from The Birds or Psycho. TV spinoffs include a “Simpsons” version, which features a poisoned donut as a weapon, and a “Golden Girls” version, in which the suspect did not commit murder, but ate the last piece of cheesecake.

Game curator Ricketts says Agatha Christie’s bestselling mystery novels, which came out around the same time as Clue, likely boosted the game’s appeal. And the game’s simplicity makes it broadly appealing to adults as well as children. “You might get away with saying it’s the fourth- or fifth-most-popular game,” after Chess, Checkers, Monopoly and Scrabble, Ricketts said—though figures vary and manufacturers are loath to disclose the total number of units sold. (Some estimates top 150 million.) “It’s still a steady seller.”

But despite Clue’s enduring success—it earned its spot in the National Toy Hall of Fame in 2017—neither Anthony Pratt nor his family reaped a significant financial reward. In 1953, Clue’s creator sold the foreign rights to the game to Waddington’s after the game manufacturer told him that it was not selling well. In return, he received 5,000 pounds.