Short answers, pulled from the story.
Samuel Morland was the first documented double agent during the Wars of the Three Kingdoms between 1639 and 1651. He lived a life of calculated duality by convincing two opposing governments that he was their most loyal servant while secretly feeding the other side the very secrets that could destroy them.
Juan Pujol García became the only British citizen to receive the Iron Cross from Nazi Germany by creating a fictional network of 27 sub-agents to feed the German Abwehr lies during World War II. His elaborate ruse known as Operation Fortitude convinced Hitler and his generals that the Allied invasion of Normandy would take place at Pas-de-Calais rather than Normandy.
Kim Philby defected to Moscow in 1963 after infiltrating the highest levels of British intelligence including MI6 and the Foreign Office as a member of the Cambridge Five. The betrayal began in the 1940s and continued until 1963 when Philby left for the Soviet Union.
Oleg Penkovskiy provided the West with critical intelligence about Soviet missile capabilities and the placement of nuclear weapons in Cuba during the Cuban Missile Crisis of 1962. His work is credited with saving millions of lives by allowing the United States and the United Kingdom to make informed decisions during the crisis.
Vitaly Yurchenko is considered a re-doubled agent because he defected to the United States only to re-defect back to the Soviet Union where he was executed. This unique case involved a high-ranking KGB officer who was initially captured by the CIA and forced to become a double agent before escaping back to the Soviet Union.
Phạm Văn Đắc operated as a triple agent by pretending to be a double agent for one side while he was truthfully a double agent for the other while working for the Viet Minh, the French, and the British. He managed to maintain the illusion of working for multiple sides while actually playing them all against each other.