A "replacement child," narrowly defined, is a person who is intentionally conceived because an older sibling has recently died. Such substitutes must endure the lifetime burden of competing with a lost and often idealized child. Because it is almost impossible for such persons to please their parents, they easily become confused and frustrated, and in worst-case scenarios, pathological.
One of the ways in which the "replacement child syndrome" manifests itself concerns the matter of self-identity. An adult "replacement child" might wonder, Who am I exactly? He might find himself, especially if he has been raised from his earliest days as if he were someone else, uncertain of his own boundaries.
The great comic actor Peter Sellers, was a classic replacement child. At birth, Sellers was named Richard Henry, but his parents, curiously, always called him Peter, after an older stillborn brother. And Peter he remained. Why would his parents do such a thing? Would it not effect a child to be called not by his own name but by the name of a missing brother?
Sellers is famous for his ability to subsume his identity into the role he played. He said that "If you ask me to play myself, I will not know what to do. I do not know who or what I am" -- because even when not acting, he was always Richard Henry playing the part of Peter.
To confuse him all the more, Sellers' father, who was Anglican, and his mother, who was Jewish, sent him to Roman Catholic schools.