The ID Monster From Forbidden Planet, 1956
"Ask a film fan for a list of the truly intelligent, well-made science fiction films of the 1950s, and you'll most likely get a fairly short list. Topping that list, however, will probably be MGM's classic, Forbidden Planet. Based, at least in part, on William Shakespeare's 1610 play, The Tempest, Forbidden Planet tells the story of a rescue mission sent to the planet Altair IV to find any trace of the missing Bellerophon expedition. What they find is Dr. Edward Morbius and his now-grown daughter Altaira, along with a terrifying invisible monster that seems set on destroying the rescue crew just as it did the Bellerophon party. To bring the invisible Monster from the Id to life, MGM made a deal with Disney studios to borrow one of their chief animators, Joshua Meador, and a crew of artists, marking the very first occasion that Disney had loaned their talent to another studio. Meador and his team developed a radical new method of animation to create the Id Monster, seen only against the discharge from an electrical fence and the crew's blaster fire. Rather than rely on traditional cell animation, in which each frame is painted on a clear acetate sheet, Meador had each frame drawn in graphite on animator's paper. Then, each of these frames was shot using high contrast film, from which a negative image was extracted and composited over the positive image. The result was a weird, roiling creature, the perfect representation of all man's basest desires. Offered here is one of the original animation drawings used in the filming of the movie, a stunning portrait of the Id Monster." - quote and image source.
Here's a screenshot from the film showing how the creature appeared in the movie...
Below is a conceptual drawing for a supposed remake of Forbidden Planet I found on flickr.
The following 3 photographs are from a detailed sculpture of the Id monster created by Tony McVey. This version takes the id monster away from the meatball with legs and fangs look into a more anatomically correct, if that's even possible, abomination. You can view the page these works were found at the Menagerie Productions website.
And a few more sculpted interpretations of the Id beast I found on google.