In Creed, Adonis uses the surname Johnson before adopting the Creed name. He is introduced as Adonis “Donnie” Johnson, using his biological mother’s surname while trying to build a boxing identity separate from his famous father.
Adonis is Apollo Creed’s son, born from an extramarital relationship and raised for part of his childhood in foster care and juvenile detention. Apollo’s widow, Mary Anne Creed, eventually takes him in and raises him. Even after learning his parentage, Adonis initially resists the Creed name because he wants his achievements to belong to him rather than to his father’s legacy.
He fights under “Johnson” in the early part of the 2015 film, including his bout with Leo “The Lion” Sporino. Later, world light heavyweight champion Ricky Conlan’s team offers him a title opportunity on the condition that he fight as Creed. Bianca encourages him to accept the name. His choice is not an error or a separate character detail: Johnson marks his initial independence, while Creed represents the legacy he eventually embraces.