Mark Twain's "A Dog's Tale" is the story of a Presbyterian dog that goes through the ups and downs of the typical dog's life, as well as that lived by dogs who are used for experimentation by science. The narrator and protagonist of the story is Aileen Mavourneen, the dog, who shares with us her thought and view on life. The description that is showed in the question is that of Mr. Gray, a scientist and the second owner of Aileen. This character is the antagonist as he shows the inhumane side of animal experimentation. Thus, the answer is A) The Antagonist.