Peter Kurten
Even though it has been 66 years since “M” was first released, no audience today will have any trouble understanding why Lorre’s portrayal of Beckert — modeled on the real-life Peter Kurten, the “Monster of Dusseldorf” — made him world-famous. When Lorre stalks his tiny victims, he is a figure of primal terror.

Hans’ first line, to Elsie. In the film’s first scenes, Hans is seen luring Elsie Beckmann, a little girl, with a balloon and is later confirmed to have killed her offscreen. Later, police investigations are shown establishing that there is a serial child murderer on the prowl, Elsie being the ninth victim.

Peter Lorre (born László Löwenstein; June 26, 1904 – March 23, 1964) was a Hungarian-American actor. Lorre caused an international sensation in the Weimar Republic-era film M (1931), directed by Fritz Lang, in which he portrayed a serial killer who preys on little girls.

Berlin
Plot. In Berlin, a group of children are playing an elimination game in the courtyard of an apartment building, using a chant about a murderer of children.

His first film at Warner was The Maltese Falcon (1941), the first of many films in which he appeared alongside actors Humphrey Bogart and Sydney Greenstreet. This was followed by Casablanca (1942), the second of the nine films in which Lorre and Greenstreet appeared together….

When we finally see his face, Beckert is revealed as a soft young man, baby-faced and nervous. One of them surreptitiously marks him by drawing an “M” (for “morder,” German for “murderer”) on his own hand in chalk and clapping Beckert on the back.

Lorre had suffered for years from chronic gallbladder troubles, for which doctors had prescribed morphine. Lorre became trapped between the constant pain and addiction to morphine to ease the problem. It was during the period of the Mr. Moto films that Lorre struggled with and overcame his addiction.