Anemoi four Anemoi and several minor wind gods are involved in the defense of Mount Olympus against Kronos (the Titan Cronus), the first series's chief antagonist. Both the Greek and the Roman forms of the Anemoi appear in Riordan's second series. Boreas is a central character in "The Lost Hero", and his children Khione, Calais, and Zetes continue to have important roles throughout the series. He resides in Montreal, and is described as "sturdily built...with dark purple wings" when in his Greek form, and as "taller and thinner" when Roman. "Notus/Auster appears in "The House of Hades" as a counselor of
Greek mythology subterranean house of Hades and his predecessors, home of the dead. Influences from other cultures always afforded new themes. According to Classical-era mythology, after the overthrow of the Titans, the new pantheon of gods and goddesses was confirmed. Among the principal Greek gods were the Olympians, residing on Mount Olympus under the eye of Zeus. (The limitation of their number to twelve seems to have been a comparatively modern idea.) Besides the Olympians, the Greeks worshipped various gods of the countryside, the satyr-god Pan, Nymphs (spirits of rivers), Naiads (who dwelled in springs), Dryads (who were spirits of the trees),