Narcissistic personality disorder (NPD) occupies a unique intersection between clinical psychopathology and modern leadership, with its roots tracing from mythological archetypes to contemporary diagnostic frameworks. This entry explores the duality of narcissism—grandiose and vulnerable subtypes—and their distinct neurobiological, developmental, and psychosocial underpinnings. Epidemiological data reveal NPD’s higher prevalence in men and in competitive sectors such as business and politics, where traits like charisma, decisiveness, and self-promotion are systematically rewarded. Subtype comorbidities, including overlaps with antisocial and borderline personality disorders, further complicate diagnosis and treatment. Neuroimaging studies implicate dysfunction in the anterior insular cortex and prefrontal circuits, underpinning the empathy deficits and self-referential thinking characteristic of NPD. Developmental theories highlight the role of early caregiver dynamics and achievement-oriented environments in shaping pathological narcissism. Despite not being formally classified as a disability, NPD’s pervasive interpersonal and occupational impairments align with disability frameworks, raising ethical questions about medicalization versus accountability. Evidence-based interventions remain limited, with psychotherapy, particularly psychodynamic, cognitive-behavioral, and mentalization-based approaches, offering gradual improvement for some individuals. In leadership contexts, NPD traits can drive both innovation and dysfunction: Operational strengths such as resilience and boldness are offset by impulsivity, ethical lapses, and erosion of institutional trust. Transactional relationships and hostility toward criticism undermine team cohesion and long-term organizational health. This entry concludes by advocating for systemic reforms that prioritize accountability, transparency, and collaboration to counterbalance the societal risks posed by pathological narcissism in leadership roles.