Cryovain was a young white dragon that tried to take over the area surrounding Phanden and Aldrigvinter in 3E448, leading to the events of Dragon of Icespire Peak that culminated in his defeat at the hands of the Phanden Four.
He is unchanged from his portrayal in the actual 5e adventure, although in Abmarah he is the son of the dragon Krahloraan.
Born somewhere in the deep northern wastes of Skion, Cryovain was too power-hungry and was chased out of the north by his father, Krahloraan.
He ended up trying to take over the area surrounding Icespire Peak, and tried to garner the respect and command of the orcs that lived in the area. Through the god Gunian, he was connected to Ian Hubert through a vision. He challenged the party multiple times, and froze over Phanden during their first meeting.
He presided over the Siege of Axeholm, watching the orc army from far away. When the Phanden Four finally challenged him at Icespire Peak, they first had to deal with the Stone-Cold Reavers who Cryovain had hired. He was finally brought down by a combined effort of the party, the orc Grannoc, as well as a local manticore. He was finally slain by Volrath Steelefist using a dragon-slaying sword.
Cryovain's small reign of terror is but a footnote in the history of the region, and the Phanden Four are considered local heroes in and around Aldrigvinter. Later during the events of The Search for Volrath, Volrath was targeted by Krahloraan who sought revenge for Cryovain's death, even though he did not much care for his son.
3E363 - Cryovain is hatched somewhere in Skion, and is the son of the dragon Krahloraan.
3E448 - Cryovain tries to take over the area around Phanden and Aldrigvinter, but is defeated by the Phanden Four during DoIP.