In Fritz Lang's 1931 film M, who played Hans Beckert?

In Fritz Lang’s 1931 film M, Hans Beckert is played by Peter Lorre.

Lorre portrays a child murderer whose crimes create panic in an unnamed city clearly modeled on Berlin. The police investigate through fingerprinting, handwriting analysis and surveillance, while organized criminals launch their own search because the police raids are disrupting their businesses. The unusual parallel manhunts give M the structure of an early procedural thriller.

Beckert’s most recognizable signature is his whistling of “In the Hall of the Mountain King,” from Edvard Grieg’s Peer Gynt. The melody functions as a leitmotif, warning viewers that the killer is nearby. Lorre could not whistle the tune himself, so the sound was dubbed. His performance, especially Beckert’s desperate courtroom-like plea that he cannot control his urges, became the film’s defining achievement.

M was Lorre’s first major starring role and helped establish him internationally, though it also contributed to his being typecast as sinister characters. Gustaf Gründgens, one of the listed alternatives, plays the criminal boss known as Der Schränker—not Beckert. The film was Lang’s first sound picture and premiered in Berlin on May 11, 1931.