John Acton, 1st Baron Acton, KCVO DL (10 January 1834 - 19 June 1902) was an English Catholic historian, politician, and writer. He was the only son of Sir Ferdinand Dalberg-Acton, 7th Baronet and a grandson of the Neapolitan admiral Sir John Acton, 6th Baronet. From 1837 to 1869 he was known as Sir John Dalberg-Acton, 8th Baronet. He is perhaps best known for the remark in a letter to an Anglican bishop, "Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men.