Pandorus Omnisiens was a powerful English Spark, who, three hundred years before Agatha's time, led a cabal ✣ of rebellious nobles in an unsuccessful attempt to overthrow the throne of England. In the process of this, they set in motion some vast process which is still causing the island nation to slowly sink into the sea. How they did this, and what they hoped to accomplish, is unknown, both in-universe and out. As the strip's plot has come and gone from England, it is unlikely there will be any answers any time soon.
Girl Genius