Vellath is a dragon hatched in Westeros by Elaena Targaryen and Daemon Targaryen, the grandparents of Danae Targaryen, Aeslyn Targaryen, and Rhaegar II Targaryen. He was commanded by Rhaegar II Targaryen until his death in the third era.
It was after Daenerys Targaryen failed to reclaim the iron throne and upon the loss of her dragons in Westeros that she fled to Braavos with little to her name but three dragons eggs from Drogon, Viserion, and Rhaegal. With the loss of her dragons the magic needed to hatch the eggs disappeared and at that point, the Targaryen dreams of retaking the Iron Throne were replaced with the harsh realities of simply trying to survive. They worked to amass a modest wealth in Braavos and lived there quietly for many years.
Sibling-spouses, Elaena and Daemon Targaryen, inherited the three eggs and returned their house to poverty and ridicule in Westeros. They sought to bring the dragons of old back into the world and sacrificed their first three children to the flame. The sacrifice of blood and fire was needed in order for men to orchestrate the hatching of dragon eggs and soon there were three small dragons in the world once again. However, the dragons had to be placed in hiding and they remained small in size compared to the dragons of old.
Three of Elaena and Daemon's living children inherited the dragons upon the passing of their parents. The siblings Naerys Targaryen and Maekar Targaryen married and gave birth to Danae and Aeslyn, while their brother fathered Rhaegar off a distant cousin. Maekar commanded Persion until the day he died, while Aeslyn's dragon was previously commanded by her mother Naerys. Upon the death of Maekar, Danae took control of Persion. All three dragons had to remain in hiding as House Targareyn had no followers, no armies, and very little land. They remained small and relatively passive for many years.
Prior to the First Era
When King Harys Baratheon discovered that Rheagar was in possession of a dragon due to the boy's carelessness, he ordered the Targaryen be sent to the Wall, though he allowed him to take Vellath with him. Vellath was always the smallest of the three dragons, only the size of a large dog, and unable to breathe fire. It is believed that Harys found him to be amusing, which is why he permitted Rheagar to keep the dragon.
Vellath proved to be disobedient to his master. Though loyal, he often disregarded commands and chose to do as he pleased.
It was believed that much of the reason young members of the Night's Watch elected Rhaegar as Lord Commander was because they were intrigued by his dragon and his ancestry.
When Rhaegar was executed, Vellath went mad with grief, breathing fire for the first time and wounding several brothers of the Watch before fleeing beyond the Wall.
Despite Artos Harclay's efforts to track the dragon, Vellath remained at large beyond the wall.
"Could you at least give us a fire? No? Stupid lizard." - Rhaegar II Targaryen