Hi. Through the context of your question, we can say that you are referring to "The Monkey's Paw" which tells the story of a family who had to face serious consequences after using a mystic monkey paw to fulfill wishes.
This monkey paw was brought to this family by Sergeant-Major Morris and it is this character who introduces the powers and dangers of this monkey paw. This makes Sergeant-Major Morris a very important character for the story and it is because of this importance that the author introduces Sergeant-Major Morris.