From Destinypedia, the Destiny wiki
The Cryptochrons are a now-defunct order of Warlocks. Their leaders were known as the Oneiromantic Circle; one member of this group was known as the Sybil. Rekkana, a member of the Kentarch 3, was a Cryptochron.
Following Osiris' exile from the City, the order was disbanded and its members banished from the City. However, the Circle persisted after their banishment, and would later direct Rekkana on a mission to enter the Black Garden along with the other members of the Kentarch 3.