The five sentient artifacts, or simply "Sentients", are ancient mystical objects which have some degree of consciousness. These artifacts were used by ancient Keepers as a safeguard against corruption. When placed in certain landmarks or "receptacles" built into the City, they would activate the Final Glyph and destroy all glyph magic. Presumably this could only be done by the One True Keeper.
It is unlikely that the artifacts themselves were created at the same time or for a single purpose. The Trickster is credited with the creation of Gruliac's Crown, whereas the Chalice bears the trademark of The Builder. The Paw and the Eye are both associated with the Trickster, but may have their origins elsewhere, whereas the Burrick's Heart may be of purely tectonic nature.
Before the construction of the City streets and monuments, the five artifacts were gathered by early prophetic Keepers and imbued with a will of their own. Five Keepers were sacrificed in the process, possibly becoming a part of the sentients. It was hoped that the desire for self-preservation would prevent the misuse of the Last of all Glyphs, as its activation would mean their demise. Only the Eye uses telepathic speech to communicate with Garrett, although a number of unused voice files suggest that both the Heart and the Crown should possess this power as well.
The sentients are generally sadistic in personality, toying with mortal minds and bringing havoc and destruction wherever they go. They do, however consent to fulfil their benevolent purpose at the conclusion of TDS.