Henry John Temple, 3rd Viscount Palmerston, KG, GCB, PC (20 October 1784 - 18 October 1865) was a British statesman who served twice as Prime Minister of the United Kingdom in the mid-19th century. He was in government office almost continuously from 1807 until his death in 1865, beginning his parliamentary career as a Tory and concluding it as a Liberal.

He is best remembered for his direction of British foreign policy through a period when the United Kingdom was at the height of its power, serving terms as both Foreign Secretary and Prime Minister. Some of his aggressive actions, now sometimes termed liberal interventionist, caused great controversy at the time, and remain so today.

For the first twenty years of his career, Lord Palmerston was known as a man of fashion, and some of the most humorous poetical pieces in the New Whig Guide were from his pen. At that time he remained a subordinate minister without influence on the general policy of the cabinets in which he served, though he was entirely devoted, like his friends Peel and Croker, to the Tory party of the day. Lord Palmerston's political roots indicate that he should not be considered a pure Whig, still less a Radical Whig. He was a politician of the old English aristocratic type: liberal in his sentiments, favourable to the march of technological progress, and entirely opposed to the notion of democratic government in Britain. He was sometimes referred to by the nickname "Pam" .