Jugo (重吾), was being held at Orochimaru's North Base, which is also where most of Orochimaru's secret research was conducted. Suigetsu can't stand Jugo and comments that one of the reasons he had to retrieve Zabuza Momochi's sword was because of him. Karin notes that Jugo is mentally unstable, a view confirmed by images of Jugo muttering to himself over who he will kill next, which he determines by gender sometimes.(Wikia)