Fedora

Fedora was the codename for Aleksey Isidorovich Kulak (1923–1983), a KGB-agent who infiltrated the United Nations during the Cold War. While working in New York, Kulak contacted the FBI and offered his services. Kulak told his American handlers there was a KGB mole working at the FBI, leading to a decades-long mole hunt that seriously disrupted the agency. It's not clear whether Kulak was acting as a double agent supplying false information or whether his information was legitimate.