Shrek was not the first film to be made using only CGI technology. That was Toy Story, in 1995. But it was the first time film-makers had tried to create realistic human characters. One of these characters was Princess Fiona. To make her move as realistically as possible, the film-makers first created her skeleton on the computer. They added muscles and told the computer how the muscles should work. Then they added her skin. But she still needed one thing-a voice.