Hedy Lamarr (/ˈhɛdi/; born Hedwig Eva Maria Kiesler; November 9, 1914 – January 19, 2000) was an Austrian and American actress and inventor. After a brief early film career in Czechoslovakia, including the controversial erotic romantic drama Ecstasy (1933), she fled from her first husband, Friedrich Mandl, and secretly moved to Paris. Traveling to London, she met Louis B. Mayer, who offered her a film contract in Hollywood. Lamarr became a film star with her performance in the romantic drama Algiers (1938). She achieved further success with the Western Boom Town (1940) and the drama White Cargo (1942). Lamarr's most successful film was the religious epic Samson and Delilah (1949). She also acted on television before the release of her final film in 1958. She was honored with a star on the Hollywood Walk of Fame in 1960.

At the beginning of World War II, along with George Antheil, Lamarr co-invented a radio guidance system for Allied torpedoes that used spread spectrum and frequency hopping technology to defeat the threat of radio jamming by the Axis powers. This approach, conceptualized as a "Secret Communication System," was intended to provide secure, jam-resistant communication for weapon guidance by spreading the signal across multiple frequencies, a method now recognized as the foundation of spread spectrum technology. However, the technology was used in operational systems only beginning in 1962, which was well after World War II and three years after the expiry of the Lamarr-Antheil patent. Frequency hopping became a foundational technology for spread spectrum communications. Its principles directly influenced the development of secure wireless networking, including Bluetooth and early versions of Wi-Fi, which use variants of spread spectrum to protect data from interception and interference.

Lamarr was born Hedwig Eva Maria Kiesler in 1914 in Vienna, the only child of Gertrud "Trude" Kiesler (née Lichtwitz) and Emil Kiesler.

Her father was born to a Galician-Jewish family in Lemberg in the Kingdom of Galicia and Lodomeria, part of Austria-Hungary (now Lviv in Ukraine) and was, in the 1920s, deputy director of Wiener Bankverein, and at the end of his life a director at the united Creditanstalt-Bankverein. Her mother, a pianist and a native of Budapest, in the Kingdom of Hungary, had come from an upper-class Hungarian-Jewish family. She had converted to Catholicism and was described as a "practicing Christian" who raised her daughter as a Christian, although Hedy was not baptized at the time.

As a child, Lamarr showed an interest in acting and was fascinated by theater and film. At the age of 12, she won a beauty contest in Vienna. She also began to learn about technological inventions with her father, who would take her out on walks, explaining how devices functioned.

Lamarr was taking acting classes in Vienna when one day, she forged a note from her mother and went to Sascha-Film and was able to have herself hired as a script girl. While there, she had a role as an extra in the romantic comedy Money on the Street (1930), and then a small speaking part in the comedy Storm in a Water Glass (1931). Producer Max Reinhardt then cast her in a play entitled The Weaker Sex, which was performed at the Theater in der Josefstadt. Reinhardt was so impressed with her that he brought her with him back to Berlin.

However, she never actually trained with Reinhardt or appeared in any of his Berlin productions. Instead, she met the Russian theatre producer Alexis Granowsky, who cast her in his film directorial debut, The Trunks of Mr. O.F. (1931), starring Walter Abel and Peter Lorre. Granowsky soon moved to Paris, but Lamarr stayed in Berlin and was given the lead role in No Money Needed (1932), a comedy directed by Carl Boese. Lamarr then starred in the film which made her internationally famous.

In early 1933, at age 18, Lamarr was given the lead in Gustav Machatý's film Ecstasy (Ekstase in German, Extase in Czech). She played the neglected young wife of an indifferent older man.