Dressed as Portrait

Others dress up as characters to participate in the plot, but he dresses up as the background... Is there anyone with a more miserable life than him? Perhaps, now is not the time to dwell on this matter. He should quickly learn "How to Make a Qualified Portrait" first, so that he will not be treated as a dangerous item by the administrator Filch or others. But the more critical issue is that the portraits in the wizarding world are all alive. He doesn't know the name of this portrait. Long black hair, green eyes - who hung a mirror opposite his painting, so needy, so grateful - on the ancient but still bright canvas, a young man in a gorgeous cloak smiled at himself in the mirror. There were three curved ancient Greek letters at the top of the frame, and eight more curved Greek letters below~~ Only in the far right corner of the canvas, there are two slanted and gorgeous English letters: S. S. Well, after glancing at the lace cuffs, at least the only thing that was certain now was that he was definitely not the potions professor, and that professor would never tolerate the existence of a portrait of him wearing such clothes. So, who is he? Purpose: Heart knots are more difficult to solve than curses