Johnny Blake, played by Edward G. Robinson, was based on real-life New York City policeman Johnny Broderick (c.1896-1966) aka "The Duke" or "the toughest cop on Broadway", while Al Kruger, played by Barton MacLane, was based on notorious gangster Dutch Schultz.
The film was so successful at the box office that it gave Edward G. Robinson the clout to negotiate a new contract with Warner Bros., which gave him rights of story and script approval and allowed him to make one movie per year for another studio.
First of five feature films starring both Edward G. Robinson and Humphrey Bogart. The other four being Kid Galahad (1937), The Amazing Dr. Clitterhouse (1938), Brother Orchid (1940), and Key Largo (1948).
This film was made as part of Warner Brothers' response to the Production Code Administration and the Legion of Decency, which had condemned the studio's previous gangster movies with Edward G. Robinson and James Cagney as glorifying the criminal life. In response, Warners had both actors make crime movies with their characters on the right side of the law with Cagney playing an FBI agent in 'G' Men (1935) and Robinson playing an undercover cop here.
In the five films Robinson and Bogart made together Robinson killed Bogart once, Bogart killed Robinson once, and they killed each other twice.