Tomas Milian played both leading roles in the film, portraying twin brothers Vincenzo Marazzi ('Il Gobbo', The Hunchback) and Sergio Marazzi ('Er Monnezza'), a dual performance he also wrote the dialogue for.

The film is the fifth and final entry in the shared Tanzi/Moretto/Monnezza universe and marks the last collaboration between director Umberto Lenzi and actor Tomas Milian.

The character of Il Gobbo had previously appeared in Lenzi's earlier film The Tough Ones (Roma a mano armata), where this film promotes him to protagonist status; his name was changed from Vincenzo Moretto to Vincenzo Marazzi.

The Sergio Marazzi 'Er Monnezza' character was first played by Milian in Lenzi's Free Hand for a Tough Cop and was later reprised in Destruction Force by director Stelvio Massi.

The Il Gobbo character may have been inspired by the real-life postwar Roman criminal Giuseppe Albano, nicknamed 'Gobbo del Quarticciolo', who was previously depicted in the 1960 film Il gobbo.

The breakup between Milian and director Lenzi was partly caused by a moralistic monologue about the wealthy classes; Lenzi wanted to cut the scene in editing, but Milian insisted on keeping it as his contract gave him that right.

The psychiatric hospital where Er Monnezza is committed was actually filmed at the former Marcigliana orphanage, now abandoned, though the film presents it as the historic Santa Maria della Pietà hospital in the Monte Mario district.

During the attempted robbery scene on Via Bissolati in Rome, a cinema marquee is visible advertising Alberto Sordi's film Un borghese piccolo piccolo, then playing at the Cinema Fiamma.

The film features two songs by Antonello Venditti, 'Sora Rosa' and 'Roma capoccia', which are also referenced in the dialogue; the character Il Gobbo is portrayed as a fan of Venditti and even quotes his lyrics from 'Sora Rosa'.