Grimms are several families of special people, warriors and hunters, who possess incredible powers, such as being able to see the true form of Wesen, even when the Wesen don't want them to. For centuries they have placed it upon themselves to police and hunt the Wesen population, to protect normal humans from the unknown threat around them.
During the Fourth Crusade, knights in service to the Seven Houses participated in the sack of Constantinople. These knights' exact numbers are not specified. The knights brought back a treasure from Constantinople so powerful, that they feared it coming into the possession of their masters. They hid the treasure and created a map in seven parts. ("Bad Teeth") Despite this have been Grimms for much longer than this, the eariest know one was alive in the first century AD ("Volcanalis").
The knights are the earliest known Grimms, and the ancestors of all modern Grimms. These knights were needed to keep the Wesen in line that made up the brunt of the Royals' Army. The Brothers Grimm, were descended from these knights. It is not clear if the term Grimm originates with the brothers or predates them.
Over the next several centuries, the Grimms served as the (usually) freelance police of the Wesen world, dispatching those who could not live in peace with humans (by contrast, the Verrat enforced the internal rules of Wesen society). As a general rule, it was the responsibility of the Grimms to hunt down "the bad ones", those aggressive and malicious Wesen who preyed on humans or other Wesen. The majority of Grimms were only exposed to the Wesen community through these malcontents, leading some of them, namely the Endezeichen Grimms, to consider all Wesen abominations that needed to be exterminated.
It appears that Grimms were involved in the Council of Walenstadt in 1521, where the Gesetzbuch Ehrenkodex, or the rules set to prevent Wesen revealing their true form was set up, as Monroe describes the event as "a Grimm event too" and there were details about it in one of Nick's Grimm Diaries.
The problem of over-zealous Grimms likely led to the creation of the Reapers, an order dedicated to eradicating them in a "who watches the watchers?" situation.
At some point the Grimms became aware of the Coins of Zakynthos and their inherent resistance to them; knowledge of the Coins was included in Grimm archives and individual Grimms were encouraged to seize the Coins and keep them safe.
When Europeans began to colonize the Americas, Grimms were present early on to document and defend against the New World's previously unknown Wesen.
By the 21st century, Grimms were feared almost without exception by the entire Wesen community. In Portland, Oregon, a single Grimm, Nick Burkhardt, has become aware of his abilities and seems to be redefining what the Wesen thought they knew about the Grimms.
Grimms are tasked with policing the creature world, making sure that those who harm humans are stopped. For this reason many wesen mistrust or fear them, even having their own set of Wesen fairy tales warning wesen children about the Grimms. Grimms possess superior fighting skills, and good heads for observation and uncanny instincts for people and their personalities, even besides their ability to sense the supernatural. So police work seems a rather good fit, as is law.
In Cat and Mouse, it is revealed that, although most Grimms broke with the Royal Houses centuries ago, Grimms occasionally work for the Seven Royal Houses and with the Verrat, helping to enforce order among the wesen. This is another reason why even a sole Grimm can inspire so much fear from wesen: the prospect of bringing the wrath of a Royal Family upon themselves if they do anything to an enforcer.
Within a single family group, not all members of a Grimm's family become Grimms. In some cases, entire generations can pass without any relative showing signs of their abilities, only for several Grimms to emerge in the same generation. As a general rule, females become aware of their abilities earlier than males. The Grimms themselves, or at least the Kessler/Burkhardt branch of the family, did not know why this was. ("Bad Teeth")
Although the majority of the Grimms discussed so far are of European descent, Grimms seem to be found worldwide, as the episode "Tarantella" involves a European Grimm meeting a Japanese doctor with all the abilities of a Grimm on a train in Singapore. However, documentation of New World species of wesen appears to have been conducted by European Grimms. It is not clear if all Grimms are genetically related (though it is implied, as on all occasions Nick's referred to any Grimm inquestion, as his "ancestors"), and if so, how many generations back the relationship goes.
Grimms seem to have preference for decapitation and there are many references to them cutting off their victim's head.
- Jacob Ludwig Carl Grimm (January 4, 1785 – September 20, 1863) and Wilhelm Carl Grimm (February 24, 1786 – December 16, 1859), The Brothers Grimm, German Philologists, Lawyers, and Capturers of Folklore. Jacob and Wilhelm are a part of the Grimm heritage, and they are Nick's ancestors, in the series.
- Robert McCormick (July 22, 1800 – October 25, 1890), a British Grimm and a naturalist. Hired by Captain Fitzroy as a surgeon and naturalist during a visit to the Galapagos Islands, the same visit that would lead to his underling Charles Darwin eventually developing the theory of evolution through natural selection. However, McCormick discovered, documented, and dispatched a creature he named Genio innocuo.
- Eduardo Grimm (? - after 1936), a Spanish Grimm who escaped to Madrid during an invasion by the Verrat. He seems to have held some sympathy for the Verrat's victims and recorded their nature as a warning to future Grimms. ("Cat and Mouse")
- Marie Kessler (1958 - 2011), an American Grimm, Nick's Aunt, and librarian who, along with her sister, hunted Wesen since they were teenagers. Prior to her death, she had become notorious among the Wesen inhabiting the Pacific Northwest. ("Pilot") ("Bad Teeth")
- Nick Burkhardt (1982 - ?), an American Grimm. He is a homicide detective in the Portland Police Bureau in Oregon. He learned from his Aunt Marie in 2011, that he is the descendant of a long line of hunters, the Grimms, who protect mankind from rogue Wesen. ("Pilot")
- Crawford Grimm (? - ?), who executed a Lausenschlange in Vienna, possibly during the reign of the Austro-Hungarian Empire. ("Of Mouse and Man")
- Kelly Burkhardt (nee Kessler) (? - ?), an American Grimm and Nick's Mother, who is the guardian of the Coins of Zakynthos. Nick believed that she, along with his father, Reed Burkhardt (? - 1994), died in a car accident when Nick was 12. Marie told Nick that his parents had been murdered. ("Three Coins in a Fuchsbau") ("Woman in Black") ("Bad Teeth")
- Mr. Kessler, Kelly Burkhardt's father (? - ?), Nick's grandfather and possible German Grimm, who became ill and bequeathed 17 trunks of Grimm memorabilia to his daughters, Kelly and Marie. He taught them about Wesen from the age of 10 to prepare them for what might come, and took them hunting at the age of 18. ("Bad Teeth")
- Mrs. Kessler, Kelly Burkhardt's father's mother (? - ?). ("Bad Teeth")
- Hilda, Kelly Burkhardt's father's mother's mother (? - ?). ("Bad Teeth")
- An unnamed probable Grimm, who was beheaded near the Schoonselhof in Antwerp, they have not found his head--it was probably Reapers. ("Plumed Serpent")
- Jose Maria Lopez Diego y Grimm (? - ?), a Grimm, who encountered a Murciélago in the upper Amazon and defended himself using a Murciélago Matraca. ("Happily Ever Aftermath")
- Hasegawa (? - ?), a Japanese doctor and possible Grimm. It is known he "shared...abilities" with a Grimm whom he traveled with on a steamer from Singapore. He passed along a scroll written in Japanese describing his encounters with a Spinnetod. ("Tarantella")
- 7 Unnamed Knights (13th Century Grimms) - Ancestors of all modern Grimms, even Nick. Originally, they worked for the 7 Royal Families to help them keep the Wesen in check. They were also on the Fourth Crusade when they sacked and burned Constantinople, and hid the treasure, that they took from it, along with another mysterious artifact of great power. ("Bad Teeth")
- Unnamed, probably Spanish Grimm, who was a Conquistador, and traveled with Cortez's expedition to South America in 1519, hearing the stories of La Llorona, he went to try and kill her, only to fail, and be killed by her. ("La Llorona")
- Unamed, Roman Grimm, who was alive in 79 AD, he investigated Volcanalis's activities in Pompeii, and was the first Grimm to document the demon, with the help of the high priest of Vulcan, he claimed the volcano and investigated the victims. He then fled with the high priest, just before Vesuvius erupted. Back in Rome he further researched Volcanalis, and found his activities caused the Volcano to errupt. ("Volcanalis")
- A young female Viennese Grimm (living) shown in "Volume 1 Number 1".
- Main article: Endezeichen Grimm
Endezeichen Grimms are the worst type of Grimms there is; they are ruthless, xenephobic and sadistic Grimms, who savagely torture and murder Wesen, not caring if the Wesen in question are good or bad.
Grimms possess many powers, the most used one is their ability to see Wesen for what they really are, but only if the Wesen is startled, scared, angered, stressed or something else happens that disrupts the Wesen's concentration.
Assumedly, Wesen are able to recognize Grimms because a Grimm responds to the morphing, since the only times when they never noticed Nick witnessing them shift before him were when they were distracted, preoccupied, or not in any way giving Nick their full attention. However, there may be another means of identification that we have not seen yet as even when Nick keeps his face passive upon seeing a Hässlich - as he did in "Leave It to Beavers" - the Hässlich still knew who he was. If this recognition of him is because Nick is well known in Portland's Wesen community or not is still up for debate. It is possible that Wesen identify Grimms not by the way they react to when they Woge, but by being able to see their image being reflected off the Grimm's eyes. Nick mentions that none of his ancestors wrote about this trait, and hypothesizes that they can naturally sense when he recognizes them. ("Quill") However, it has been shown that the Wesen only recognizes the Grimm in question if they see the Grimm observe them woge. ("Of Mouse and Man") ("Quill"). Sight may not have anything to do with a Grimms' ability to sense Wesen as Nick was able to detect the presence of Rosalee Calvert and Andre, despite having been temporarily blinded by the latter. ("Mr. Sandman")Grimms also possess superhuman physical traits, such as strength, durability, agility, reflexes, and speed. This allows them to go toe to toe with any Wesen, except Siegbarste, and survive things that would kill a normal person. Nick was able take on a Skalenzahne (one of the strongest known Wesen) and defeat it. His aunt, despite dying of cancer, and weakened by the drugs, was still able to kill her human attacker, and showed no fear to Monroe. Grimms' strength can also be measured in the fact they can casually take down Wesen who possess superhuman strength, such Jagerbar's or Klaustreich, and can easily overpower humans. Grimms' durability is particularly notable; several times Nick has shrugged off blows from creatures with incredible strength. For example, when facing a Schakal, the creature smashed a toaster around his head, but he recovered in seconds. ("Woman in Black"). He was even able to escape from a beating with a Siegbarste, with the worst of his injuries being a few bruised ribs.
It has also been shown that the blood of a Grimm can destroy the animal part of a Hexenbiest. ("Love Sick") In essence, the Hexenbiest becomes human after this and is no longer a part of the Wesen world. It is currently unknown if this will work on other members of the Wesen world.
Grimm also possesses greater resistance to temptation than humans, and are the only beings able to resist the temptation of the Coins of Zakynthos.
As well as this, Grimms seem to have a natural aptitude for fighting, particularly against Wesen, and with ancient and medieval weapons. They also possess incredible observation abilities and keen instincts. There also seems to be some natural aptitude in the Grimm lines of artistic talent as there are many detailed pictures in Aunt Marie's books from the other Grimms and Nick shows an aptitude for drawing as well. And when blinded, Nick's hearing is enhanced to the point of hearing from far away as Nick was able to hear Rosalee coming and Hank's conversation with Wu on the phone despite being far away. He was also able to hear a fly buzzing on the ceiling and to destroy many thrown fruit with his kanabo when he and Monroe were testing his hearing. ("Mr. Sandman")