A thesis and an introduction, though similar, are not exactly the some thing. An introduction to a paper, or essay, defines an overview of what the essay will be about. This functions as a map of what the essay will be about, outlining the main points and arguments to be laid out for the reader. The thesis, on the other hand, singularly defines what the essay's main point will be. A introduction, then, uses numerous sentences to "tell" readers what the focus of the essay will be. The thesis, on the other hand, defines in one to two sentences the direct focus of the paper.
Bilbo Baggins, the hero of J.R.R. Tolikien's The Hobbit, is not a hero at the beginning of the text. In fact,it is his journey over the course of the text which defines him as an epic hero. Beowulf, on the other hand, is a known epic hero entering into the action of the text. As the true epic states, the epic hero must enter into the text in the midst of turmoil. Beowulf, true to heroic form, enters into the text amidst Hrothgar's troubles with Grendel. He has heard of Hrothgar's woes and travels to the Danelands in order to help the mighty king. Bilbo, on the other hand, is sought out by Gandalf (who wishes him to take upon an adventure).
Therefore, an introduction to a compare and contrast essay regarding the heroic nature of both Bilbo and Beowulf would address the similarities and differences between the two characters. The introduction would define, generally, the main points behind the adventures of each character, the challenges each face, and the adherence to the traits true of the epic hero. A possible thesis would address that not all epic heroes are self-made (as with Beowulf) through their own persuasion. Instead, some may become heroes because of the strength others see in them (as with Bilbo).