I think one of the hallmarks of a good actor is their ability to blend into their character so much that the actor disappears and all that remains is the character that they’re performing. This isn’t as easy as it sounds and many actors can’t quite pull this off. A classic example is Keanu Reeves. Now, I really like Keanu. He and I share the same birthday so of course, Virgos are awesome. But I don’t think anyone would take the position that he’s got a versatile acting range. He’s Keanu Reeves playing Neo. He’s Keanu Reeves playing Ted. He’s Keanu Reeves playing Johnny Utah. He’s Keanu Reeves playing Jonathan Harker (ugh). He’s Keanu Reeves playing Le Chevalier Raphael Danceny (double ugh). His characters are a translucent coat that changes his hue (slightly) but leaves him still quite visible.
On the other hand, some actors disappear so completely that you forget all of the memorable roles that they’ve played. No one exemplifies this more to me than Gary Oldman. His is chameleonesque. A master of disguise. A shapeshifter. At times I wonder if he’s human or a T-1000.