Seraphon

Seraphon is the terrifying Black Dragon that the Witch King Malekith rides to battle upon.

After a band of Shades found a clutch of unguarded eggs, deep within the Spiteful Peaks mountain range, Malekith ordered that the eggs be brought back to Naggarond. There they were ritually tended by the priestesses of Khaine for almost a century until they hatched. Seraphon was the first to emerge and before the Witch Elves could stop him, he had destroyed many of the other eggs. Malekith was impressed by the Dragon's ruthless instincts and decided that he would take the Dragon as his own mount.

The few remaining Dragon hatchlings were all given to Malekith's most favoured generals. These nobles have spent many decades training to fight with these monstrous beasts in preparation for the Witch King's next assault on Ulthuan.

Now Malekith feels the time is right for his people to wage war once again. The Witch King and Seraphon will fight at the fore of a highly trained flight of Black Dragons, whose surprise strike attacks will ravage the shores of the Old World and cities of Ulthuan.

Source

 * Warhammer Armies: Dark Elves (7th Edition) -- pg. 57