"wrath") is a special person who possesses incredible powers, such as being able to see the true form of Wesen even when the Wesen don't want them to.
According to Monroe, they can see an "infinite darkness" in a Grimm's eyes that reflects the Wesen's true nature.
However, modern Grimms can use sunglasses to avoid detection from Wesen via eye contact.
This name has since fallen out of fashion and is now only used by traditional Wesen such as Gelumcaedus.
Grimms possess many powers; the most commonly used one is their ability to see Wesen when they are woged, but only if the Wesen is startled, scared, angered, or stressed, or something else happens that disrupts the Wesen's concentration.
The rage stage comes much earlier, and the Cracher-Mortel is unable to control them.
They also still possess their Grimm powers, making them very dangerous.
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 in question, they are referred to as his "ancestors"), and if so, how many generations back the relationship goes.
During the Fourth Crusade, seven knights in service to the Seven Houses participated in the sack of Constantinople.
These knights were needed to keep the Wesen in line that made up the brunt of the Royals' Army.
A Grimm's ability to detect Wesen is not limited to sight; Nick has demonstrated the ability to detect the presence of Rosalee Calvert and Andre, despite having been temporarily blinded by the latter.