Dragon Mages

Into every generation of Caledorian nobility, a handful of Dragon Mages are born, Elves who have a sensitivity not only to magic, but also to the minds of slumbering Dragons. Many nascent Dragon Mages only recognise their destiny when their sleep becomes haunted by dreams of fire and blood, in which they ride Dragons the colour of the setting sun. Such dreams mark the dying days of a mage's tutelage, for they herald an impetuousness that is ill-suited to the study of anything other than Fire Magic.

When able, the Dragon Mage journeys to the sulphur-clogged caverns below the mountains of Caledor, there to awaken a slumbering Sun Dragon to serve as his steed. This is a process that normally takes months, or even years, yet a Dragon Mage can fully awaken a Dragon with but a whisper of its name. Thus begins a bond that lasts until either mount or rider is slain in Ulthuan's defense.

Source

 * Warhammer Armies: High Elves (8th Edition) -- p. 47