Usually male, Wardens are the sworn guardians of Witches. They are skilled fighters and tacticians. Each witch has a Warden. In witch families where a Dud is born, the Dud is usually trained to become a Warden.
Witches pick their Wardens, usually in the Novice stage of their training.
Kelly's father, Marcus, is her mother's Warden.
Wardens bear silver rings with shields. Depending on their rank, the shields on the rings are different colors.
Red being for a Senior member, Green for a Novice.
The Shield rings allow the Wardens to use some semblance of magic, mainly to protect their witches. However, the shields can also detect magic too. For example, Mr. Donovan tells Kelly that his ring was unable to detect anything wrong with George.
There are families out there that were born to be Wardens. The members of these families usually sign into Contract with a specific witch family. The young Warden is assigned to a witch at a young age and when te time is right, he enters into a formal Contract with her.
Usually the proximity to said witch forms a "bond" between the two of them. This "bond" connects to the two of them, making their partnership much stronger. The Bonded Warden can sense when his witch is in danger and can even muster some form of magic to protect her.
Honor Contracts are Old World. In most cases they are no longer used. Most modern witches pick their own Wardens. Though in this case, no Bond is formed.