Stormcloud

Stormcloud was one of the dragons that belonged to House Targaryen. It was bonded with Aegon III Targaryen, though he had yet to ride it when the great civil war known as the Dance of the Dragons began.

His name is never confirmed, though he does prominently appear on-screen in the "The Dance of Dragons" Season 5 Blu-ray featurette, which matches his actions from the novels.

Biography
Stormcloud was a young dragon when the Dance began, not quite a hatchling anymore but not yet big enough for even a boy to ride.

As the war between Rhaenyra Targaryen and her half-brother Aegon II Targaryen progressed, she decided that she should send the two youngest of her five sons, who were only small boys, to safety in the Free Cities. The young Aegon III Targaryen and Viserys II Targaryen boarded the ship, taking Stormcloud with them as they set out from Dragonstone to cross the Narow Sea.

Soon afterwards, however, their ship was intercepted by an enemy fleet bearing down on the island. Aegon III escaped by desperately clutching on to Stormcloud, who was mortally wounded by an arrow bolt in the throat. Despite both his wounds and the fact that he still wasn't really big enough to carry the boy's weight, Stormcloud somehow found the strength to fly the terrified Aegon all the way back to Dragonstone. Upon landing, Stormcloud collapsed in exhaustion and soon died. His sacrifice did, however, give Rhaenyra warning of the approaching enemy fleet, leading to the Battle of the Gullet.

In the books
Stormcloud was one of the youngest dragons, too small to ride when the Dance began - though ultimately he died saving Aegon III by flying him to safety under great strain and badly wounded by arrows.

Stormcloud was bonded with Aegon III, the second-youngest of Rhaenyra's five sons, while her fifth and youngest son Viserys II possessed no dragon, only an unhatched egg. The "Dance of Dragons" Season 5 Blu-ray featurette makes a mistake with this: without giving names, it says that Rhaenyra's "youngest son" flew his young dragon back to her castle after his ship was attacked, leaving the other behind and assumed captured or dead. It even uses the same character artwork: the shortest and youngest of Rhaenyra's sons at her council scene is presumably Viserys II, wearing a red jacket, and later he is the one seen climbing off the dying Stormcloud. This is apparently just an unintentional mistake and not a conscious change to the TV continuity, and thus is disregarded.

The coloration of Stormcloud's scales is unknown.

Stormcloud was one of the youngest and smallest dragons, not quite a "hatchling" anymore but not big enough that Aegon III had attempted to ride him yet. The next largest dragon was apparently Moondancer, which belonged to his half-sister Baela Targaryen, though Moondancer was also too small to ride at the beginning of the war (though she was big enough near the end of it). Meanwhile, Rhaenyra's third son Joffrey Velaryon possessed the young dragon Tyraxes, who was big enough for short flights but deemed not worth risking in combat. Aegon II's firstborn son and daughter also possessed two dragon hatchlings, Morghul and Shrykos.

The exact lineage of the Targaryen dragons is unknown, though it is possible that the dragon eggs which several of Rhaenyra's sons hatched were laid by her own dragon, Syrax (she is mentioned as laying new clutches of eggs, implying she had previous ones). Dragons at the time of the Dance generally fell into four broad categories, possibly reflecting which generation each one was from: Vhagar was huge and last of the first-generation dragons, while Vermithor and Meleys were still large second-generation dragons. Then there were apparently third-generation medium-to-light dragons, still at least big enough to ride in war, ranging rom Sunfyre to Vermax. Below that there were the three hatchlings at the start of the war, Stormcloud, Morghul, and Shrykos, who may have been the fourth dragon generation in Westeros. This is only conjecture, however, as dragon eggs can lay dormant for many generations out of sequence - i.e. for all we know, both Vermithor and Stormcloud were hatched from eggs laid by Vhagar herself, but Stormcloud's egg hatched a hundred years later.