It goes by a multitude of names: blob, jelly, goo, ooze, grime, gelatinous cube, but the simple 'slime' is by far the reigning favorite for this ucky monster. Swallowing everything in its wake or spitting bits of goo at its enemies, the Slime is prevalent in fantasy and sci-fi, from the all-consuming Blob or S.L.I.M.E. to the cute little drop-like slimes of Dragon Quest. However, unlike most monsters this mysterious creature never appeared in legends and myths - they first showed up in the 1900s.
In 1958 a movie called 'The Blob' showed in theaters, following the story of a strange and horrific goo or slime that crashed near a small town on a meteorite. Devouring unwary townfolk, it begins to envelope the town and a couple of local people must find out some way to put a stop to this terror.
Previous to this movie, there were a couple of mentions of slime-like beings, including the Shoggoth creatures in the Cthulhu stories published around 1929. While they possessed some elements of slimes they did have some key differences (namely the ability to morph into any form and create organs and limbs at will), so although they appeared before the movie 'The Blob' and some other key jellies, they are mostly unlike a more 'traditional' slime monster.
Then in 1977 the Monster Manual was published as an accessory book to the popular Dungeons and Dragons tabletop roleplaying game by TSR. In the guide were descriptions of dozens of monsters in the game - one of which being a square-shaped slime called the gelatinous cube.
One of the most popular forms of slimes was created in 1986 with the first Dragon Quest game (known as Dragon Warrior in the US market). These slimes were cute and fun monsters, completely re-envisioning the 'slime' idea. In some Dragon Quest games they even can be friendly shopkeepers or bankers!
Slimes can be big or small, all-consuming or friendly, but in one way or another they've become a staple of the sci-fi and fantasy genres.
This little Cutie looks a lot like a silly Slime, or maybe a tiny Water Drop! :)