Acton, Baron, John Emerich Edward Dalberg-Acton, First Baron Acton of Aldenham (1834–1902), an English historian. Though he never finished a major work, he was a brilliant scholar who had a strong influence on others. Acton planned the Cambridge Modern History, but lived to edit only the first volume. He was a leader of the liberal Roman Catholics who disputed the doctrine of papal infallibility.

Acton was born in Naples, the son of a British nobleman. He was a Liberal member of the House of Commons, 1859–65. In 1869 he was created a baron. He taught history at Cambridge, 1895–1902.

Essays on Freedom and Power (1955) is one of several volumes of lectures and articles published after his death. It contains his oft quoted remark, “Power tends to corrupt and absolute power corrupts absolutely.”