“Doppelganger” is German for “double walker”, a shadow self that is thought to accompany every person.
“Of all the prostheses that mark the history of the body, the double is doubtless the oldest. But the double is precisely not a prosthesis: it is an imaginary figure, which just like the soul, the shadow, the mirror image, haunts the subject like his other, which makes it so that the subject is simultaneously itself and never resembles itself again…”
Jean Baudrillard: “Simulacra and Simulation (1981)”
Alternatively in psychotherapy terms.
“The shadow only becomes hostile when he is ignored or misunderstood.”
Carl Jung: ‘Man & His Symbols’.