Arrax was a dragon, apparently male, ridden by Prince Lucerys Velaryon during the reign of Viserys I Targaryen and at the Dance of the Dragons.
Although he grew larger every year and was big enough to be ridden, Arrax was still young at the time of the Dance of the Dragons.
According to Archmaester Gyldayn, he was faster, but also five times smaller than Vhagar. He would be pearly white with golden chest and eyes, and his flames would be yellow.