Who is Leonard Zelig from Necessary Losses and what is their importance?

Woody Allen's hero, Leonard Zelig, is a "human chameleon" with no identity of his own. He "turns into whomever he is with." In the movie Zelig, Allen's hero goes through being black, Chinese, obese, Native American, a Nazi soldier, an assistant to the Pope and part of Babe Ruth's baseball team. Viorst uses him as an example of a borderline personality, who never finds his true self, and adapts to his situation by trying to please and conform to whoever is around him, creating false selves by reading the signals and clues around him, imitating and mimicking others' realities, having no inner experience of his own. She discusses how a borderline personality can divide the good and bad in himself, in her chapter entitled "The Private I."