The 25th president of the United States - William McKinley.
McKinley was the last president who served in the Civil War. Unfortunately his second term in office was abruptly nixed by an anarchist.
I'm relatively certain that Sam Eagle from The Muppets was based off of McKinley. He's a dead ringer.
PS. I highly recommend Assassination Vacation by Sarah Vowel, who makes a lot of really interesting observations about historic presidential assassinations.