Syd Mead
According to the commentary in the DVD, Number 5 was the most expensive part of the film, requiring several different versions to be made for different sequences. Almost everything else in the film was relatively inexpensive, allowing them to allocate as much money as they needed for the robot character. Number 5 was designed by Syd Mead, the "visual futurist" famous for his work on "Blade Runner" and "Tron".