Nictis Cross was a wizard from around 1400, who tortured the wizard Sinu the Red, until Sinu was compelled to torture and kill his master. Before this, he kidnapped Sinu from the town of Tarry Hollow, where he disguised himself as a potion salesmen, and stole a bunch of money from people.
He has never been seen in the series, as he died many years before the story began.