Henry John "Harry" Temple, 3rd Viscount Palmerston, KG, GCB, PC, FRS was a British statesman, who was twice Prime Minister of the United Kingdom in the mid-19th century. Palmerston dominated British foreign policy during the period 1830 to 1865, when Britain stood at the height of its imperial power. He held office almost continuously from 1807 until his death in 1865. He began his parliamentary career as a Tory, defected to the Whigs in 1830, and became the first prime minister from the newly formed Liberal Party in 1859. He was highly popular with the British public. David Brown argues that "an important part of Palmerston's appeal lay in his dynamism and vigour".
Henry Temple succeeded to his father's Irish peerage as the 3rd Viscount Palmerston in 1802. He became a Tory MP in 1807. From 1809 to 1828 he served as Secretary at War, organising the finances of the army. He first attained Cabinet rank in 1827, when George Canning became prime minister, but like other Canningites, he resigned from office one year later. He served as foreign secretary 1830–1834, 1835–1841, and 1846–1851. In this office, Palmerston responded effectively to a series of conflicts in Europe.