Gatekeepers

The Gatekeepers of the Dreaming are three creatures who take the form of a wyvern, a griffin, and a hippogriff. They are charged with guarding the entrance to Dream's palace and notifying their master of visitors.

History
The gatekeepers are dreams whose power and authority are derived from Morpheus himself. When Morpheus was captured in Preludes and Nocturnes, they weakened and lost their ability to guard the palace or protect the Dreaming.

After the griffin was destroyed by the Furies in The Kindly Ones, the new incarnation of Dream did not remake him but asked the griffins of Greek myth to send one of their own.

Trivia

 * Despite its name, the hippogriff does not have the frontquarters of an eagle the creature is traditionally known for, instead resembles is a winged horse or pegasus.