Lewis Thornton Powell was an American Confederate soldier who attempted to assassinate William Henry Seward as part of the Lincoln assassination plot. Wounded at the Battle of Gettysburg, he later served in Mosby's Rangers before working with the Confederate Secret Service in Maryland. John Wilkes Booth recruited him into a plot to kidnap Lincoln and turn the president over to the Confederacy, but then decided to assassinate Lincoln, Seward, and Vice President Andrew Johnson instead, and assigned Powell the task to kill Seward.

William Henry Seward was an American politician who served as United States Secretary of State from 1861 to 1869, and earlier served as governor of New York and as a United States senator. A determined opponent of the spread of slavery in the years leading up to the American Civil War, he was a prominent figure in the Republican Party in its formative years, and was praised for his work on behalf of the Union as Secretary of State during the Civil War. He also negotiated the treaty for the United States to purchase the Alaska Territory.