Ysanne Isard was director of Imperial Intelligence from around 0 BBY to 7.5 ABY and de facto Galactic Empress 4 ABY – 6 ABY. Following her expulsion from Coruscant by the cosmetically superior forces of Rouge Squadron, she fled to Thyferra and made eight clones of herself so she could keep coming back in as many books as possible.
Tragically, she suffered from a unique genetic mutation that caused a fatal reaction in anyone who maintained physical contact with her for too long. She also had Ocular Exovar Syndrome. She killed many people, caused the deaths of three Imperial Governors, and Sate Pestage, along with thousands of Coruscanti during the launch of her Super Star Destroyer, Lusankya from the base of Coruscant. Many, many people died.
By the way, many Imperial men had intense crushes on her.