Daniel Edgar Sickles (October 20, 1819 – May 3, 1914) was an American politician, soldier, and diplomat.As an antebellum New York politician, Sickles was involved in a number of public scandals, most notably the killing of his wife's lover, Philip Barton Key II, son of Francis Scott Key. He was acquitted with the first use of temporary insanity as a legal defense in U.S.