Ulf the White

Ser Ulf the White is an unseen character. He is long dead by the time of the series. He was a dragon-rider for Rhaenyra Targaryen's faction during the Dance of the Dragons.

Biography
Ulf was one of the Targaryen bastards from Dragonstone recruited as a dragon-rider for Rhaenyra Targaryen due to his heritage. After Aegon II's loyalists besieged Tumbleton, Rhaenyra sent Ulf and fellow dragon-rider Hugh Hammer to relieve her garrison. However, the two instead burned Rhaenyra's troops and defected to Aegon's side, drinking and whoring with his troops after taking Tumbleton.

Reference

 * "The Dance of Dragons (Histories & Lore)"