The amorphous creature is a common trope

Trope (literature)

A literary trope is the usage of figurative language in literature, or a figure of speech in which words are used in a sense different from their literal meaning...

 in science fiction

Science fiction

Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

. Usually it is depicted as a living mass of jelly-like substance that can take any shape it wants. Perhaps the most familiar example is the title alien from the movie The Blob

The Blob

The Blob is an independently made 1958 American horror/science-fiction film that depicts a giant amoeba-like alien that terrorizes the small community of Phoenixville, Pennsylvania...

, but other examples include the vermicious knids from Charlie and the Great Glass Elevator

Charlie and the Great Glass Elevator

Charlie and the Great Glass Elevator is a children's book by British author Roald Dahl. It is the sequel to Charlie and the Chocolate Factory, continuing the story of young Charlie Bucket and eccentric candymaker Willy Wonka as they travel in the Great Glass Elevator.Charlie and the Great Glass...

, a giant pasty mass of protoplasm

Protoplasm

Protoplasm is the living contents of a cell that is surrounded by a plasma membrane. It is a general term of the Cytoplasm . Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and...

 found in Venusian jungles in one of Stanley G. Weinbaum

Stanley G. Weinbaum

Stanley Grauman Weinbaum was an American science fiction author. His career in science fiction was short but influential...

's few short stories, and the Shoggoth

Shoggoth

A shoggoth is a fictional monster in the Cthulhu Mythos. The being was mentioned in passing in sonnet XX of H.P...

s from the Cthulhu Mythos

Cthulhu Mythos

The Cthulhu Mythos is a shared fictional universe, based on the work of American horror writer H. P. Lovecraft.The term was first coined by August Derleth, a contemporary correspondent of Lovecraft, who used the name of the creature Cthulhu - a central figure in Lovecraft literature and the focus...

.

Amorphous creatures are to be distinguished from shape-shifter

Shapeshifting

Shapeshifting is a common theme in mythology, folklore, and fairy tales. It is also found in epic poems, science fiction literature, fantasy literature, children's literature, Shakespearean comedy, ballet, film, television, comics, and video games...

s that can change their appearance to mimic whatever they like, such as the T-1000

T-1000

The T-1000 is a fictional nanomorph mimetic poly-alloy assassin and the main antagonist in Terminator 2: Judgment Day controlled by the series main antagonist Skynet. The T-1000 is portrayed primarily by Robert Patrick; however, being a shape-shifter, the T-1000 is played by other actors in some...

 from Terminator 2: Judgment Day

Terminator 2: Judgment Day

Terminator 2: Judgment Day is a 1991 science fiction action film directed by James Cameron and written by Cameron and William Wisher Jr.. It stars Arnold Schwarzenegger, Linda Hamilton, Robert Patrick, and Edward Furlong...

, or the title character from The Thing.