Unidentified decedent, or unidentified person, is a corpse of a person whose identity cannot be established by police and medical examiners. In many cases, it is several years before the identities of some UIDs are found, while in some cases, they are never identified. A UID may remain unidentified due to lack of evidence as well as absence of personal identification such as a driver's license. Where the remains have deteriorated or been mutilated to the point that the body is not easily recognized, a UID's face may be reconstructed to show what they had looked like before death. UIDs are often referred to by the placeholder names "John Doe" or "Jane Doe". In a database maintained by the Ontario Provincial Police, 371 unidentified decedents were found between 1964 and 2015.

Forensic facial reconstruction is the process of recreating the face of an individual from their skeletal remains through an amalgamation of artistry, anthropology, osteology, and anatomy. It is easily the most subjective—as well as one of the most controversial—techniques in the field of forensic anthropology. Despite this controversy, facial reconstruction has proved successful frequently enough that research and methodological developments continue to be advanced.