Question: Who founded the metal band who's retrospective box set of albums was entitled Trolsk Sortmetall 1993-1997?
{'answer': 'Ulver (Norwegian for wolves) are a Norwegian experimental musical collective founded in 1993, by vocalist Kristoffer Rygg.', 'supporting_facts': [['Trolsk Sortmetall 1993-1997', 0], ['Ulver', 0]]}