Gavarex was the main and oldest dragon of the purported builder and first king of Drakonia, Aenarion Dragomárus. He was reputed to be the largest and strongest dragon to ever exist; his very wingspan could blot out the sky for a city, and his breath could incinerate thousands of men at a time.
Gavarex was an immensely large black dragon, with fire hot enough to make brick harden -- one of the things he was said to do when Aegor I built Drakonia. He had massive horns, and wings that darkened the sky for close to a mile everywhere he flew. He was descended from Messeneth, the dark counterpart of The Dragonlord.
Gavarex was also subject to scrutiny of existence, like that of Aegor I's, but several large dragon skeletons in Doras Edrossi point to his existence.