Rat

s are a significant species of Teenage Mutant Ninja Turtles lore. Every version of the character Splinter is a rat.

Rats are non-fictional terrestrial  native to Earth, where they exist in vast numbers, having permanently colonized every continent except Antarctica. Feral rats live in the shadow of virtually all human societies, opportunistically scavenging from humans' food, garbage and waste while also sometimes functioning as vectors for the spread of certain human diseases. Because of this, many human cultures have come to associate rats with infestation, uncleanliness and pestilence in general. Most major cities, like New York City, have large feral rat populations; humans usually consider their present undesirable, so city rats spend most of their time in environments humans rarely visit, such as sewers, storm drains, inside the walls of buildings, and so forth.

Rats are also recognized for their intelligence and resourcefulness. They can be raised as pets (called s), and pet rats raised in a clean well-cared-for environment tend to be healthier, grow larger and live longer than feral rats. The and  versions of Splinter began their lives as Hamato Yoshi's beloved pet fancy rat.

Rats are also important to scientific research in the form of s where they function as similar analogues to human biology. This is because humans and rats (along with other, other rodents and s like s) are more closely genetically related to each other to each other than they are to any other mammals. , they are grouped together in the , also known as Supraprimates.  The  is the reincarnation of, but started his rodent life as an otherwise ordinary laboratory rat at StockGen.

Certain other recurring fictional characters and technological inventions in Teenage Mutant Ninja Turtles are associated with rats.

Most versions of Baxter Stockman invented robotic machines called Mousers, whose primary function is to hunt and eat rats (making them a danger to rat characters like Splinter), but can also be directed for most insidious tasks like assassinations, bank robberies, the intentional collapse of city buildings, and mayhem in general.

The Rat King is also strongly associated with rats. Most versions of this character have a supernatural influence over rats, having the ability to compel them to swarm specific areas or against specific targets. Some versions of the Rat King can use this same power of persuasion to compel ordinary rats to be his eyes and ears, acting as spies and informants. However, most versions of the Rat King are themselves actually humans rather than rats.