During the second draconic war, a farmer at Burden's Rest found Solus' egg and cracked it open. Solus then served as the Dragon-Rider of mount and created his namesake. He appears in the game in Orange Eyes in the Blood of the Kasans node.
Although the Dragron-Rider is called that name because of Solus. Several other dragons were ridden by him and frequently used as his mount during battles. A few examples of which are War Wyverns (if one considers a wyvern a dragon), Lysimache the Dreamer, Fey Folk Flutterer, Timon the Yellow, Nestor, Tiresias, Andromeda, Echidnina-Slayer's Mount (a gnome toy dragon, not a actual dragon), Erebean drake, battle drake, clockwork dragon (gnome construct dragon), Echnidnina-Slayer's War Mount (bigger version of the regular mount with spikes), Void-Knight's Drake (also known as Bash, mother of Andromeda), Snow Warrior Drake, Drunken Angel's Wyvern (though technically a wyvern), Necromancer's Bone Dragon (undead dragon), Fossilized Bone Dragon (undead dragon), Drake of the glorious Dawn, Dragon Illusion Drake (just as how Paxon Greengaze could transform into a bear, the Dragon-Rider could transform into a dragon), Masterer's Wyvern (again, unless you do not consider Wyvern dragons), Magma Drake (most reknown of which is Imryx the Incinerator), Drake of the Breaking Dawn, Erebean gore drake, and many others.