The correct answer is Beowulf/the dragon.
Beowulf is the main character in the epic poem "Beowulf," which means that he is the protagonist. Antagonist is a bad character, who is usually the protagonist's worst enemy. In the beginning of the poem, the antagonist was Grendel, but at the end, it was the dragon.
Thesis definition: a statement or theory that is put forward as a premise to be maintained or proved
So,
Without having a recognizable thesis, your reader will not fully understand what point you are trying to get across. Furthermore, your writing will seem to have no meaning or purpose, and will not inform the reader. To clarify, if you do not have a recognizable thesis, your writing would be pointless.
look for first person words. I, me, my mine, etc. referring to oneself