Giants, also called Jotunn or Gigantes, are a species of xenoform related to the Olympians. Some giants have also intermarried with the Aesir and Vanir. Descended from Ymir, son of Ouranus, the giants were banished from Olympus by the Sky Father, who was disgusted by his son's ugliness. They were banished to the desolate ice-world that the Greeks called Tartarus and the Norse called Niflheim. From there, they explored Yggdrassil and took up residence in the worlds of Muspelheim and Jotunheim, in the process encountering the Norse gods. Kronus recruited an army of giants in order to overthrow his father but banished them back into Tartarus once he had secured the the throne. Zeus allowed the giants, along with their cousins the Cyclopes and the Hecatonchires, to return to Olympus, but banished the giants back to Tartarus after they attempted to take the throne of Olympus for themselves.