Daniel Edgar Sickles (October 20, 1819 – May 3, 1914) is a colorful and controversial American politician, Union general in the American Civil War, and diplomat.

As an antebellum New York politician, Sickles is 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 is acquitted with the first use of temporary insanity as a legal defense in U.S. history.

He becomes one of the most prominent political generals of the Civil War.

At the Battle of Gettysburg, he insubordinately moves his III Corps to a position in which it is virtually destroyed, an action that continues to generate controversy; despite this, he is eventually be awarded the Medal of Honor in 1897.

His combat career ends at Gettysburg when his leg is struck by cannon fire.

After the war, Sickles commands military districts during Reconstruction, serves as U.S. Minister to Spain, and eventually returns to the U.S. Congress, where he makes important legislative contributions to the preservation of the Gettysburg Battlefield.