The Were-Riders (sometimes written Were Riders or Wereriders) were first introduced in Year of the Unicorn.
Appearance: Were-Riders, as first introduced, have black hair and green eyes. They probably resemble the Old Race in other features.
Life Span: Though the life span of the Were-Riders is not mentioned, they have lived for centuries at least. This is backed up by Kethan's swordmaster mentioning having trained Herrel when he was young. In Year of the Unicorn, Herrel hints to Gillan that the Were-Riders are over a thousand years old.
Power: Were-Riders seem to have a lot of Power. Beyond their ability to shape shift they can easily cast very complicated illusions and separate a person into two entities. The exact limits of their powers is unknown. Herrel also implies to Gillan in Year of the Unicorn that they can bend time as it doesn't seem to flow at the same rate for them as it does for the Dalesmen of High Hallack. In fact this may be true of the defensive barrier around Arvon itself. They also demonstrate the ability to create powerful wards, seduction spells and travel into the spirit realm.
Other: How much of their shape shifting is illusion and how much is real is debatable. They can all shapeshift into animals, usually related to a heraldic image: pard, lion, hawk, eagle, horse, boar, wolf, fox, bear, badger, etc. They are also apparently able to assume other shapes as well, though they do so less often and these secondary forms seem more like an illusion than reality (their change into a beast seems to be real shape-shifting, not illusion).
Gryphon in Glory mentions there are twenty banners for the Were-Riders in their Lodge in the Waste. Whether this means there are twenty Were-Riders or merely twenty forms is unclear. Also possible is that only twenty were in residence at that time and the others were off on a mission of some kind. Though there are thirteen brides from the Dales, Herrel mentions there are nearly twice that number of Riders. Bloodspell mentions there are nearly forty Riders, though at least two die in that story. Given the length of time they traveled and any possible losses in their fight against the Alizonders during the invasion of High Hallack, it seems safe to say there are probably at least twenty-six Riders left.
Were-Riders seem to have an affinity for having names that begin with 'H'. Kethan is an exception, but he wasn't named by his true parents. Kethan's reliance on his pard belt seems to be due to the spells laid on him before he entered the Youth's Tower. Despite what is shown in The Warding of the Witch World he has started to learn to transform without it by the end of The Jargoon Pard and with practice probably wouldn't need it at all.
The novella Were-Wrath, if set in the Witch World, shows Farne, whose mother was human and father Were, initially needing an animal fur belt to assist his transformation. When he fully accepts his heritage and takes up his sword of power, the belt disintegrated. His sword is similar to the sword Herrel uses to channel power in The Jargoon Pard. It's possible Farne is descended from Aurek & Derora from Rite of Failure as Greer and the northern lands mentioned in Were-Wrath are similar to High Hallack and Arvon, though they are not named as such. It's possible they may be located in the Waste where Rite of Failure takes place.
There are no female shape shifters among the Riders, though both Were-Hunter and Were-Flight introduce female shifters. One is a young woman from Earth (Glenda) with a special ring that initiates her transformation after arriving in Arvon. The other (Khemrys) is the daughter of a Were-Rider (Herwydin) and a Daleswoman (Tirath). Both young women change into large cats and meet male Riders that also change into large cats (Harwin, son of Kildas & Harl, and Harlyn, whose parents names are unmentioned).
The Were-Riders were a created race, the Adept who built the Grey Tower fused his most loyal retainers with animals so they could transform into them at will. We, the Women implies that the Were-Riders were originally men of a race the Falconers attacked when they entered the Witch World and drove from their land, their women taken as wives. The men eventually ended up in Arvon and took service with the Adept who made them into the Were-Riders.
It is unclear why the Were-Riders did not each have a bride. The number of "twelve and one" brides may have to do with the original geas of their banishment from and return to Arvon.
Names, forms, and brides
Despite the emphasis placed on the Brides, only five of them are mentioned by name in Year of the Unicorn: Kildas, Solfinna, Alianna, Aldeeth, and Marrime (whose place was taken by Gillan). The others are not mentioned in this book or any other.
Among the Were-Riders there are also only a few names and forms mentioned. Both Year of the Unicorn and Bloodspell have names and forms, though exactly how canonical Bloodspell is may be debated. Were-Flight and Were-Hunter also have some lineages (which, again, could be debated as to being cannonical or not). Names or forms in bold are from Year of the Unicorn & Gryphon in Glory, names or forms in italics are from "Bloodspell". Names and forms that are from "Were-Hunter", "Were-Flight", and "Rite of Failure" are noted when they appear:
Herrel [Snow Cat]2
Hewlor [Gray Wolf]
Helder [Black Wolf]5
[Tawny red and black-spotted Cat]
["a snouted and armored lurker of the river"]6
Hannon [ Black Bear ]7
Hathor [ Mountain Elk ]
[ Red Wolf ]
[ Desert Lion ]
Harlyn [large cat with molted head and smoky-tipped tail]9
Harwin [snow leopard]10
Aurek [golden pard]12