No portrait. His own likeness isn't the point. The rose is.
Ancient and Powerful. Some consider him to be the most powerful wizard to ever have lived.
Cursed, his attitude changed. He was less concerned by others. He stopped caring altogether about anything other than his magic. Obsessed with, not power, but knowledge. He sought out ancient tombs, for ancient spells and forgotten magics. During this time he was simple know as "Raven". A dark wizard who even the gods left alone.
The Silver Rose
A face was never the point of the name.
William Silverrose is never drawn. Wherever his story needs an image, it gets a rose instead, silver-edged and glowing where his legend is spoken of kindly, black and bladed where it isn't. The distinction isn't subtle, and it isn't supposed to be: the white roses belong to the archmage the School was named after. The black one belongs to "Raven," the alias he carried during the dark insanity.
The Creation
His old friend, made into something the world had never seen before.
No stats for Golaric here. In William's story, he's myth more than he is a playable character.