The boy who never grows up in J. M. Barrie's story is Peter Pan.
Peter Pan is a fictional boy created by Scottish author and playwright J. M. Barrie. He lives in Neverland, where he leads the Lost Boys and encounters fairies, pirates, mermaids, and children from London. His defining trait is his refusal or inability to grow up, making him a symbol of perpetual childhood and youthful escape.
Peter first appeared in Barrie's 1902 novel The Little White Bird, in chapters later published separately as Peter Pan in Kensington Gardens. Barrie then made him the central character of the stage play Peter Pan; or, The Boy Who Wouldn't Grow Up, which premiered in London in 1904. The familiar prose version, Peter and Wendy, followed in 1911.
Michael, John, and Wendy are not alternative names for Peter. They are members of the Darling family who travel with him to Neverland: Wendy is their older sister, while John and Michael are her younger brothers. The character's many later adaptations, including Disney's 1953 animated film, helped make “Peter Pan” the standard answer to this question.