In the psychological thriller film Joker, released in 2019 and starring Joaquin Phoenix in the first role, another possible origin story for this iconic character is reported. Above all, it brings us medical elements for the understanding of the development of this complex character. Contrary to other interpretations, we discover a lonely, timid and uncharismatic man (Arthur Fleck). He seems to be suffering from psychobehavioral disorders and seems depressed. There is a strangeness in his behavior along with social withdrawal. He suffers from fits of laughter that occur at socially inappropriate times. He also suffers from psychotic symptoms with visual delusions. We learn through the film that he was a beaten child, psychologically and physically abused with severe traumatic brain injury (TBI). The uncontrollable outbursts of laughter, behavioral and psychotic disorders followed these elements. As a neurologist, I was intrigued by these symptoms. I have explored the neuropsychiatric symptoms complicating TBI from which he seems to suffer and which have been reported in the literature. We can assume that the Joker is suffering from neuropsychiatric sequelae related to childhood TBI involving the frontotemporal regions and, in particular, the lateral aspect of the left frontal lobe. The movie Joker has medical significance and covers social aspects of medicine and health care. First, it allows us to discuss whether psychotic disorder due to TBI should be considered a neurobiological syndrome. More broadly, albeit fictitious, it asks us about the management of patients with neuropsychiatric illness, which is a public health problem. It also reminds us that semiological descriptions of patients with neuropsychiatric disorders have served as inspiration for many authors.