Simple. As soon as you head to Tamoril, the dragon npc at magician quarter in Yalahar, and ask him about the first dragon he will response you this:
Player: First Dragon
Tamoril: The First Dragon? The first of all of us? The Son of Garsharak? I'm surprised you heard about him. It is such a long time that he wandered Tibia. Yet, there are some rumours.
Tamoril: It is told that the First Dragon had four descendants, who became the ancestors of the four kinds of dragons we know in Tibia. They perhaps still have knowledge about the First Dragon's whereabouts - if one could find them.
Tamoril: The names of these four are Tazhadur, Kalyassa, Gelidrazah and Zorvorax. Not only were they the ancestors of all dragons after but also the primal representation of the draconic incitements. About whom do you want to learn more?
That being said, the First Dragon is the son of Garsharak. Yet making it kinda unanswered at the same time.