Aaron Burr
Matthew Smith
In 1804, Aaron Burr and Alexander Hamilton dueled, resulting in Hamilton's death. Burr was Vice President at the time, and Hamilton's federalists attacked Burr in newspapers and journalism, defaming him. Hamilton hated Burr so much, he aided Jefferson in becoming president rather than Burr. After the killing, Burr was tried with murder and then treason, being acquitted of both.
Importance
At the time, the practice of dueling was being outlawed in several states, and Burr's acquittal caused controversy. Also controversial was the fact that he killed a founding father (that's pretty bad). Burr's Democratic Party he created to get himself in office gained considerable power in later years.