Aaryonar guards the entrance to the main ring of the northern wing. He will come to the aid of any other dragons if aggro'd before he is killed except the five in the very northern hall. While it seems he will always come with his guards if they are aggro'd, he can be single-pulled from them. Beware of the guards and Aaryonar's long aggro range, and that the top step leading to him is extremely slippery.
In the Temple of Veeshan: Casts "Call of the Zero" every 10 seconds. Also casts "Cloud of Disempowerment" every 20 seconds. (Pic by: Harlee Quinn, Nox Mustale)
In the Corrupted Temple of Veeshan: See this quest entry for event information.