Answer: 1. Boston Corbett
I shot John Wilkes Booth
Lincoln's Avenger
the nickname seems subjective, so we will defer to hoosier.
Edit - Sources show that "Glory to God Man" was also a nickname used by Corbett, so clearly that is an acceptable answer to the third part of the question.
A number of players gave "Thomas Corbett" as their answer to the first part of the question and "Boston" as their answer to the third part, i.e., his nickname.
The Wikipedia article on Corbett begins by stating his name as Thomas P. "Boston" Corbett. Customarily, if you see a Wikipedia article that states someone's name in this manner, the name in quotation marks is the person's nickname. For an example, see the Wikipedia article on George Herman "Babe" Ruth. For that reason, I will accept answers saying that Boston was Corbett's nickname.
However, I do want to point out that if you read the whole Wikipedia article, it states that Corbett, after his religious conversion, changed his name from Thomas to Boston - which means that he wanted people to consider Boston to be his real name, not his nickname. A number of other sources also make this point.
Hoosier