Ian Holm, who played Ash, died in 2020, so the film used CGI to recreate his likeness, and he was voiced by Daniel Betts.
Speaking about having Ian appear in Alien: Romulus, Fede Álvarez told Entertainment Weekly, “The whole thing started with me calling the estate and talking with his widow. She felt that Ian was given the cold shoulder by Hollywood in the last years of his life, that he would’ve loved to be part of more projects after The Hobbit, but he wasn’t. So she was thrilled about the idea of having him back.”