Monsters (derives from Latin monstrum), are the eponymous creatures that Monsters, Inc., Monsters University, and their spinoffs and adaptations in other media focus on.
Unlike humans, which are fairly consistenting skin and hair colors, and body structures, monsters have a wide variety of natural physiques. Monsters can resemble an anthropomorphic animal, or can have their own, unique forms. Brock Pearson and Claire Wheeler are fine examples of this contrast; the former is very birdlike in appearance, giving him a mutant-like look, while the other is more humanoid, giving her a more alien-like appearance. Monsters of all sizes have been spotted, fat and skinny, as well as tall (and even giant) and short.
Some monsters have a head attached to a body, such as Sulley, but they may or may not have a neck. The Abominable Snowman, for example, has a head separate from his body, but he lacks a neck, or at the very least, his neck is not automatically visible. Other monsters, such as Mike Wazowski, have heads that also serve as their body. While they are fairly rare, some monsters do happen to share their body with another monster. Monsters University gives more focus to this possibility, with conjoined twins Terri & Terry being major characters, and the three-headed Kowalski sisters being shown as a singular Scarer. A monster is covered in either skin, fur, scales, or a combination of those three options. Collectively, monsters are very colorful; bright and dark shades alike are likely to be part of a monster’s appearance. Stripes and spots might also be part of a monster’s color scheme. Monsters rarely have visible noses or ears, and when they do, those body parts are usually respectively represented by a horn or fish-like fins. Fins are also used as some monsters’ equivalent to human hair, seen in characters like Don Carlton and Smitty, although other monsters, such as Roz, have humanlike hair. Celia Mae is a unique case to the hair scenario, since her “hairdo” consists of a group of sentient snakes.
Although most monsters have fairly sharp teeth, this is far from being always the case. George Sanderson, for example, has blocky humanlike teeth despite his job as a Scarer. Horns, tails, spikes, claws and wings of all shapes and sizes are also prevalent features of a monster’s appearance, and monsters usually have one of these features. However, there are cases where a monster simply lacks anything bar the bare minimum aspects of a basic body, such as Art.
The way a monster’s eyes and limbs function depends on the monster itself. The normal amount of eyes and limbs for humans (and most non-insect or marine creatures) is two eyes, two arms, and two legs. With monsters, the amount varies, and there are no strict norms about the amount of eyes and limbs a monster should have. However, it is uncommon to see monsters with an “abnormal” amount of eyes, arms, and legs. Monsters often have the usual two of at least one of these body parts, and the usual two for all of the parts is as common as having an abnormal amount of at least one of the parts. There are monsters, most notably the slug-like ones, that lack legs, and others in rarer cases, such as Harley Gerson, lack arms. However, there are no monsters that naturally lack eyes.
Monster eyes vary in color. Just like humans, the most common eye colors found in monsters are brown, blue, and green. Eyes also vary in size, with the size of an eye depending on how many eyes a monster has. For example, a Cyclops would have a large eyeball due to its singularity. In the case of multiple-eyed monsters, such as Fungus (who has three eyes), eyes are usually smaller because they need space on the face. However, there are monsters with differently shaped eyes. Waternoose, for example, has his eyes positioned in an even order (the second and fourth ones) larger than the ones positioned in an odd order (the first, third, and fifth). As mentioned beforehand, there is no expected amount of eyes a monster should have. Despite this, monsters frequently have one eye, two eyes, or three eyes. On more uncommon occurrences, a monster can be seen with four eyes or five eyes. On even rarer occasions, a monster can be seen with an even higher eye count; the highest amount of eyes seen on a monster in one of the films was twenty, on one of the witnesses of Boo’s “attack” in Monsters, Inc. There are two ways a monster’s eyes are connected to its body, they might be stuffed right into their skull, or they might be connected to a stalk. The amount of eyes a monster has is not related to the way its eyes connect to its body.
Monster limbs are also just as diverse. A monster’s arms and legs will typically resemble each other, although there are situations where this is not the case. Dean Hardscrabble, for example, has humanoid arms, but a multitude of centipede-like legs. Just like the aforementioned Hardscrabble, monster limbs can be humanlike or more animalistic. Primate-like and reptilian limbs of all sizes have been seen. If a monster’s limbs do not belong to those categories, they are likely to be tentacles instead. Hands are a different beast entirely, and they are usually amongst a monster’s more prominent physical attributes. Most monsters either have three or four fingers on each hand, with the presence of claws depending on the monster. There are cases with several fingers on each other hand, to the point of abnormality even for human standards. As for legs, they tend to be shorter than arms if they are not tentacles. This is especially prominent in more mammalian monsters such as Sulley and George Sanderson. There are cases, such as Waternoose, Chet Alexander, and Ricky Plesuski, where the legs resemble claws. Aside from that, there isn’t a lot that separate the legs from the arms aside from their biological functions. If a monster has toes on their feet, then the usual amount is three. Most monsters either have two or four arms, although some of them, like a commonly seen type of CDA agent and Rivera, have six. As for legs, the usual amount is either two or none at all. If a monster has cephalopod or crustacean features, then the amount of legs usually rises up to at least four.
Overall, monsters are a very diverse species, with the uniqueness of body type, color scheme, and amount of eyes and limbs being a source of pride for many a monster.
According to a DVD bonus feature of Monsters, Inc, Monstropolis was founded after all of the monsters who once co-existed with humans were all chased off the mainland and eventually moved to an big island on an unknown place where they have lived ever since. The only way for them to enter human-inhabited areas is via closet doors.
Monsters have been scaring humans for at least nine centuries, as the prestige scaring school Monsters University was founded in 1313.