Some of the greatest talents ever to grace the film industry, including the likes of Daniel Day-Lewis, Cate Blanchett and Christian Bale, despite being massive stars and celebrities, manage to become completely unrecognisable every single time they're on screen.
Not only does an actor's own performance cement that immersion, but the makeup, hair and, of course, prosthetics, help bring a character to life on the big screen. Allowing actors to convincingly resemble real people or transform them entirely into an alien figure, prosthetics have helped actors give their best performances as well as gain critical recognition, perhaps most recently evident in Gary Oldman's oscar-winning transformation into Winston Churchill.
That said, sometimes an actor undergoes a physical transformation for a role and it just... doesn't work. Whether the prosthetics themselves look terrible or actively obscure a star's performance to the point where it leaves audiences wondering why the studio shelled out for such a big name at all, not every actor has survived a stint in the makeup chair.