<p>Digital doppelgangers are individualized, continuously updated digital representations of a person constructed from behavioral, physiological, and contextual data streams, including smartphone metadata, wearable sensor outputs, social media activity, and environmental sensors. Whereas conventional digital twins in physical medicine primarily replicate anatomical structures and physiological parameters, psychiatric digital doppelgangers are designed to capture dynamic mental states, emotional trajectories, and behavioral pathways through aggregated multimodal digital traces. Preliminary research suggests potential clinical utility across several domains, including earlier detection of depressive and bipolar episodes, risk stratification for suicidal crises, and individualized treatment planning; however, most applications remain at the feasibility and proof-of-concept stage and have not yet achieved prospective clinical validation. Implementation raises substantive challenges, including informed-consent complexity under fluctuating decisional capacity, algorithmic bias arising from non-representative training datasets, diagnostic ambiguity in the interpretation of behavioral signals, inequitable access to required technology infrastructure, and the risk of reconfiguring the therapeutic relationship into a surveillance mechanism. Responsible development requires interdisciplinary collaboration among clinicians, technologists, ethicists, regulators, and patient communities, alongside robust ethical frameworks, prospective validation regimes, and genuine patient partnership throughout the development cycle. Digital doppelgangers represent a conceptually distinct but adjacent framework to digital twins, digital phenotyping, and AI-driven cognitive science models; their trajectory in psychiatry depends on whether technological ambition is matched by equally rigorous governance and a primary commitment to patient welfare.</p>