The Shari Tcha'kla was a group of 30 Vulcans whose raison d'être was to monitor members of the Twelve Families to ensure that they hewed to a Surakian ideal of thought and behavior. Those who did not were deemed v'tosh ka'tur -- Vulcans who rejected the teachings of Surak, and were without logic. Such individuals were banished from Vulcan society.
They called themselves the "Guardians of Vulcan", but while their primary task was being the guardians of the Vulcan way, they also were the physical guardians of members of the Twelve Families.
Legends are unclear as to when the Shari Tcha'kla were founded -- either during Surak's lifetime by the philosopher himself, or after his death.
Three months before the Enterprise was to conclude its first five-year mission under James T. Kirk in 2270, Spock met Sudak, a member of the Shari Tcha'kla who convinced him that undertaking the Kolinahr would be beneficial to both Spock's relationship with Kirk, and to all Vulcan. (Absolute Horizon)