Grimm

Grimm (グリム, Gurimu), or the Creatures of Grimm, are the universal antagonists of the RWBY series, inhabiting various parts of Remnant.

They are described as "creatures of destruction" and lack a soul; hence, they are unable to use Aura. They are also drawn to feelings of negativity- such as envy, sadness, loneliness, and hatred- often congregating towards the source of these emotions.

At one point, ancient cultures believed that Grimm were animals possessed by evil spirits or were the spirits of once tortured animals.

"For as long as humanity can recall walking the surface of Remnant, so do they remember this wicked force."
 * —Salem, About Grimm.

Anatomy and Design
In the episode "The Next Step" the births of Grimm are depicted as Beowolves emerge from a black pool in Salem's Domain. However, most of humanity is unaware of the origins of Grimm. Ancient human cultures believed the Grimm were animals possessed by evil spirits or even the tortured spirits of animals themselves. Further study has disproved this theory over time, however, due in part to the discovery of even more horrific misshapen species of Grimm which have no animal counterparts (such as Creeps). With the discovery of new types of Grimm every day, scientists are left with more questions than answers.

Grimm come in a variety of shapes and sizes; the latter appears to be a factor of age. They are said to be the only creatures without souls, thus being deprived of the use of Aura, but they make up for this with strength, durability, and savagery. Some Grimm even have special abilities such as possession or usage of lightning. Grimm are stated to be attracted to generally negative feelings such as sadness, hostility, anger, fear, etc.; and even congregate in areas that, although humanity has long since abandoned, still hold residual traces of these feelings.

This behavior will even lead to them to join in on an attack in progress if the humans being attacked begin to panic. Grimm typically form packs or other types of large groupings with other members of their own specific species. While some lone Grimm may stray from the pack for hours or even months, they will inevitably rejoin their group to continue their instinctive drive to hunt the people of Remnant and destroy any artificial creations associated with them.

The longer a Grimm lives, the larger it becomes, with species such as the Nevermores ranging from the size of an average bird of prey to massive pterosaur-sized beasts after hundreds of years. Although Grimm have a more reckless nature during their youth, older Grimm who have managed to survive their battles have the tendency to learn from their experiences. While sometimes requiring hundreds of years, the Grimm's accumulated experiences over the course of surviving their battles with man can cause them to begin exercising caution.

This perverse form of self-preservation can even lead them to avoid unnecessary conflicts altogether. Yet, despite this ability to learn, their instinctual hostility still remains, as shown by their preference to patrol the borders of Kingdoms for any weaknesses they might someday exploit. This demonstrates that for all their apparent intelligence, older Grimm simply use it as a means to become more effective in their singular drive and purpose of killing.

Grimm display no enmity towards normal animals, and they only clash during territorial disputes. Humans and Faunus are the only races they attack on sight. Grimm can also choose not to eat, and it is commonly believed that they do not require sustenance. When Grimm die, their corporeal form evaporates, preventing detailed anatomical or biological studies. This also means that Huntsmen that kill for sport cannot stuff and mount Grimm bodies as trophies (making replicas instead).

Also of interesting note is that Grimm usually die off when in captivity (if they cannot kill their captors or escape first), implying that they cannot be kept alive by normal means. If the theory of Grimm not needing to feed is true, it is entirely possible that they survive on negative emotions or the act of killing in itself.

Past
According to Ozpin, the Grimm were created by the god of darkness in order to destroy his older brother's creations of life. Eventually the brothers ended their feud and both created Humanity. But despite the younger god's involvement in creating Humanity, the Grimm were still left to roam Remnant and prey on them.

They have targeted Humans for as long as can be remembered, seeking to destroy them and all of their creations. At first, it seemed as though they would succeed, as Humans did not have the strength to fight them. However, Humans discovered the power of Dust, and with it, the Grimm were driven back. During this time, Humans enjoyed a time of peace and soon formed their own Kingdoms, which grew to survive and prosper. However, this time would not last indefinitely.

While Grimm are initially mindless and heedless of risk during their youths, leading them to simply attack any humans on sight, some Grimm are so powerful that they have survived to live for hundreds of years. In that time, they have evolved and learned from their experiences fighting humanity. This leads them to exhibit restraint and the patience to avoid taking unnecessary casualties in futile conflicts; instead, they stay close to humanity's borders, waiting for the opportunity to come where they can finally strike. Because of this, mankind is in ever present danger, even in times of apparent peace. Bartholomew Oobleck recounts this in the episode "Search and Destroy" when he tells Ruby Rose how intelligent some species, such as the Goliaths, have become over the years.

The Grimm have also, for many years, disrupted land-based travel and communications between Kingdoms. After the Great War of Remnant eighty years before the series begins, the invention and production of the CCT towers replace futile land-based communication systems with instantaneous wireless electronic messaging capabilities.

Additionally, the Grimm appear to be the predominant species in the world of Remnant as humans and Faunus appear to be limited to four primary pocket settlements referred to as Kingdoms, which are guarded by Huntsmen, as well as several villages with mixed success. Attempts by the Kingdoms to expand beyond their borders are often met with resistance, and even failure, as the loss of an entire sector of the city of Vale overrun by the Grimm can attest to.

Notes & Trivia

 * Grimm follow a color theme of red, white, black and a little yellow.
 * These are all the colors of the four main characters.
 * The name for the creatures of Grimm may well could be a reference to either the Brothers Grimm or Grimms' Fairy Tales, a famous classic collection of German fairy tales compiled by the brothers.
 * Additionally, the word Grimm is German for fury, wrath, fierceness or grim.
 * When killed, Grimm are known to emit smoke. It is later confirmed in the RWBY: World of Remnant episode "Grimm" that Grimm dissolve when they die.
 * The White Fang wear Grimm Masks because humans tried to make monsters out of them, so they wear the faces of monsters as a symbol.
 * All of the Grimm creatures' vocal sound effects were done by William Orendorff.
 * Cinder Fall was able to summon an unknown, Grimm-like insect from her glove.
 * RWBY: Grimm Eclipse is named after the Grimm, which serve as common enemies in the video game.
 * In the manga the Arma Gigas is described as being a Possession-Type Grimm, having been created by amalgamating several different species of Grimm.
 * According to the Volume 3 DVD Directors' Commentary, the ability of the Dragon to spawn Grimm offers a sneak peek towards their creation.