Daniel Edgar Sickles (October 20, 1819 – May 3, 1914) was an American politician, soldier, and diplomat. Born to a wealthy family in New York City, Sickles was involved in a number of scandals, most notably the 1859 homicide of his wife's lover, U.S. Attorney Philip Barton Key II, whom Sickles gunned down in broad daylight in Lafayette Square, across the street from the White House. He was acquitted after using temporary insanity as a legal defense for the first time in United States history.