John Emerich Edward Dalberg-Acton, 1st Baron Acton, KCVO DL

(10 January 1834 – 19 June 1902)—known as Sir John Dalberg-Acton, 8th Baronet from 1837 to 1869 and usually referred to simply as Lord Acton—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.

He is perhaps best known for the remark, "Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men." This idea has been tested in laboratory settings.