Banner of the World Dragon

Elven legends tell that Draugnir, Father of Dragons, was welcome in Asuryan's court as an equal, for mortal Elves and gods alike were awestruck by his might and nobility. Alas, not all the Elven pantheon were so enamoured. Anath Raema, sister to Khaine and goddess of the savage hunt, saw him as nothing more than an upstart beast to be harried and hunted as any other. Taking her spear, she pursued the Dragon through the heavens. The contest that followed shook the world to its core, rousing even wise Asuryan from contemplation. The Creator halted the battle, but came too late to save Draugnir, whose wounds were beyond healing.

With a single word, Asuryan banished Anath Raema to the Mirai forevermore. From the corpse of his fallen friend, he worked to create a new land where Elves and Dragons could live in peace, beyond the jealousies of the gods. From Draugnir's bones, he forged Ulthuan's mountains, and from the Dragon's flesh he created its broad plains. Draugnir's glittering scales Asuryan gave into the keeping of Isha. She, in turn, passed them to her mortal children, the Elves, who wrought many fabulous works with them, chief amongst them a mighty standard, woven with silver and hung with gems of all shapes and hues. This Banner of the World Dragon endures to this day, a reminder not only of the bond between the Elves and Dragons, but also of that which binds both races to their ancestral home.

Source

 * Warhammer Armies: High Elves (8th Edition) -- p. 65