“hic iacet arthurus, rex quondam rexque futurus” means

This is a Latin phrase meaning "Here lies Arthur, king once, king to be"

Explanation:

This is a phrase is the title of the first book in the series of fantasy books by T. H. White, inspired by the story of King Arthur.  The title comes from an inscription which, according to Thomas Malory's work, Le Morte d'Arthur, was written on the tomb of King Arthur: Hic iacet Arthurus, rex quondam, rexque futurus - Here lies Arthur, king once, king to be."

caliban is prospero's slave in the shakespear's play "the tempest"