Siegel was born into a family of Austro-Hungarian Jews who immigrated to the United States in 1903 and settled in Manhattan’s Lower East Side. In an effort to escape his impoverished upbringing, he drifted to the streets as a boy and took part in crimes such as burglary and organizing protection rackets for street peddlers.

Siegel later met and befriended future crime boss Meyer Lansky during his teen years, and together the two formed the Bugs and Meyer Mob, a gang that dabbled in robbery, gambling and murder. With Prohibition in full effect, the group also joined with mobster Arnold Rothstein in establishing a lucrative business running bootleg liquor along the East Coast. The young Siegel flaunted his newfound wealth by wearing expensive clothes and frequenting high-class nightclubs. By 1931, he was rich enough to buy an apartment in Manhattan’s Waldorf Astoria Towers.

As a teen, Siegel’s violent temper and mercurial personality saw friends describe him as “crazy as a bedbug.” Many soon began calling him “Bugsy” or “Bugs,” but the young gangster loathed the nickname and supposedly threatened anyone who used it. “My friends call me Ben,” he once said, “strangers call me Mr. Siegel, and guys I don’t like call me Bugsy, but not to my face.”

Siegel’s criminal reputation is steeped in myth and legend, but there is evidence that he played a role in around a dozen killings during his rise in the 1920s and 30s. When an assassin once tried to murder him by lowering a bomb down a chimney, an injured Siegel supposedly checked himself into the hospital and then snuck out and murdered the man, only to later slip back into his room, alibi intact.

Siegel is also reported to have been one of the men who gunned down Sicilian mobster Giuseppe “Joe the Boss” Masseria in 1931, and he was widely linked to Lucky Luciano and the infamous “Murder, Inc.,” a syndicate of contract killers who carried out hits for the Italian and Jewish mafias.

In the mid-1930s, Siegel moved from New York to Los Angeles and set up a new criminal empire on the West Coast. Along with dipping his toes in gambling, wire services and drugs—he may have helped establish the narcotics trade between Mexico and the United States—he also became a fixture in the Hollywood social scene.

Siegel’s tough guy persona and movie star good looks proved irresistible to celebrities, and he hobnobbed with the likes of Cary Grant, Frank Sinatra and blonde bombshell Jean Harlow, who became the unofficial godmother of his young daughter. Friends would later say that Siegel harbored a secret desire to be an actor. He was a frequent visitor to Hollywood movie sets, and once even organized a screen test for himself.

Siegel’s reputation as a celebrity gangster reached new heights in 1938 when he joined a band of Hollywood aristocrats on a bizarre schooner trip to the seas off the coast of Costa Rica. Lured by reports of buried treasure, Siegel and his fellow passengers sailed for remote Cocos Island and spent several days digging, drilling and even dynamiting hillsides in a fruitless search for it.

The harebrained treasure hunt came up empty-handed, and the group’s ship later had to be towed to Mexico for repairs after it was ravaged in a storm and left adrift. News reporters pounced on the “hell ship” story after Siegel returned to California, with some alleging that the voyage had involved a mutiny by the crew or that it had been a cover for a drug smuggling or gunrunning operation.

Siegel was arrested on suspicion of everything from possession of narcotics and firearms to murder and rape, but he was only found guilty of two minor offenses: a 1930 charge of “gambling and vagrancy” and a 1944 charge of “placing bets illegally on a horse race.” In both cases, he walked free after paying a fine.

Siegel’s most serious brush with the law came in 1941 when he was arrested for the murder of an underworld figure named Harry Greenberg. He spent time in jail, but the charges were dropped after a key state witness died under mysterious circumstances. Siegel remained a suspected criminal kingpin, however, and was later the subject of extensive surveillance by the Federal Bureau of Investigation in the years before his death.

By far the strangest chapter in Siegel’s career unfolded in 1939 when he partnered with a Hollywood socialite named Countess Dorothy di Frasso in a scheme to peddle arms to the fascist Italian government. According to historian Larry Gragg, the deal centered on a newfangled explosive called atomite, which was supposedly more powerful than dynamite. Siegel and the Countess hoped to secure a contract to sell it to dictator Benito Mussolini, but their plan went up in smoke after the atomite failed to impress during a demonstration.

Before they left Rome, the pair reportedly crossed paths with Adolf Hitler’s second-in-command, Hermann Göring, who was in town for an audience with Mussolini. Siegel, who was Jewish, would later quip that he wished he had assassinated the high-ranking Nazi when he had the chance.

In 1946, Siegel tried to turn from mobster to real estate mogul by taking over the stalled construction on a flashy Las Vegas hotel and casino known as the Flamingo. With financial backing from old pal Meyer Lansky and several other underworld figures, he eventually burned through $6 million turning the Flamingo into one of the most lavish properties on the fledgling Las Vegas Strip. The bloated project lost money during its first few months in operation, but business later picked up in the months before Siegel’s murder in June 1947, and the Flamingo became the mafia’s first major foothold in Las Vegas.

Popular legends and fictional portrayals have since characterized Siegel as a visionary who invented modern Las Vegas. But while he may have added a dose of glitz and glamour to “sin city,” there were already several casinos and hotels in operation by the time he arrived. “Ben Siegel did not invent the luxury resort-casino,” wrote Meyer Lansky biographer Robert Lacey. “He did not find the Las Vegas Strip. He did not buy the land or first conceive the project that became the Flamingo. But by his death, he made them all famous.”

On the evening of June 20, 1947, Siegel was reading a newspaper at his girlfriend’s Beverly Hills home when a gunman fired nine shots through the window with a .30 carbine. Siegel was hit by four slugs—one of which knocked an eye out of its socket—and died instantly. It was a classic gangland hit, but despite a media circus and a massive police investigation, the precise motive for the killing has never been confirmed.

Most researchers speculate that Siegel’s criminal associates were fed up with the soaring coasts of the Flamingo hotel and casino, while others say he was suspected of skimming money from the construction budget. Other theories include a mob struggle over the horse racing wire service, which Siegel controlled, or even that Siegel was embroiled in a love triangle with his girlfriend and another gangster. The identity of the shooter is also cloaked in mystery. Mob figures Frankie Carbo and Eddie Cannizarro are among the leading suspects, but the case remains open to this day.