Thlawg is the brother of Ral'Kafeel, but is not hurtful and is the same size as Kafeel, 600ft. He is known as the Gentle Dragon and fights against evil.
Thlawg is an Ice Drake, but dwarves other drakes in size, and is known as a power drake, ranging up to 600 ft high, the limit a power drake can reach. Thlawg is 600 ft high, and so is Ral'Kafeel. Thlawg, Ral'Kafeel, Smieg, Dros, and Ral'Kafool are all Power Drakes.
Thlawg hatched 500 years before the first age began. He was brought up by Ama the elven queen(picture down below), and he was unusually friendly for a dragon. At the age of 12, Thlawg had to leave as he was beginning to grow and so left Ama. Ral'Kafeel had been jealous, and thats what started their war.
During the middle of the first age, Rohan was an almighty city, and wasnt like it was now. It had huge structures that would make Minas Tirith jealous. Thlawg was forced to agree to make a siege on Rohan with Ral'Kafeel and an army of dragons. Rohan was made to dust, and Thlawg attacked Ral'Kafeel, only to be horded and overpowered by the other dragons. He retreated and made an army of Ice Eagles, and in the fourteenth age, eventually killed his brother. Thlawg would eventually live forever, and was an immortal drake.