Answer
Seán Lemass served as Tánaiste or deputy prime minister of Ireland a record three times over the course of his long political career. His first term was from 1945 to 1948, followed by a second term from 1951 to 1954, and lastly from 1957 to 1959. Notably, he served under a total of three Taoisigh or prime ministers during these periods: Éamon de Valera, John A.