Many critics agree that one of the best parts of Don Juan is Byron's sassy speaker. Take, for example, the lines where he says, "But if there's anything in which I shine,/ 'T is in arranging all my friends' affairs,/ Not having, of my own, domestic cares" (1.23). In this section, Byron's speaker says that he meddles with other people's lives because he has nothing better to do. This comment would have hit home with a lot of English readers, since English culture in Byron's time was rife with gossipers and busybodies.
As the poem continues, Byron's speaker gives more clues to make us think he is Byron himself. At the beginning of the Canto IV, the speaker says, "Some have accused me of a strange design/ Against the creed and morals of the land,/ And trace it in this poem every line" (4.5). Here, Byron seems to respond directly to critics who accused him of writing filth in his earlier Don Juan cantos. Now, it's never a good idea in poetry to confuse a speaker with the actual, biographical author. Still, the longer the poem goes, the more Byron embraces his speaker and uses the speaker to spout all his own criticisms of English people and their culture. By the end, you're practically begging the guy to stay focused on his plot.