Teresa Bagioli Sickles was the wife of Democratic New York State Assemblyman, U.S. Representative, and later U.S. Army Major General Daniel E. Sickles. She gained notoriety in 1859, when her husband murdered her lover, Philip Barton Key II, son of Francis Scott Key. At his trial, Sickles claimed for the first time in United States jurisprudence a defense by temporary insanity. He was acquitted.

Philip Barton Key II was an American lawyer who served as U.S. Attorney for the District of Columbia. He is most famous for his public affair with Teresa Bagioli Sickles, and his eventual murder at the hands of her husband, Congressman Daniel Sickles of New York. Sickles defended himself by adopting a defense of temporary insanity, the first time the defense had been successfully used in the United States.