Sidney Carton is one of the greatest unlikely heroes in literature. In the beginning, he is an immoral, despicable, and hypocritical drunk. At the end of the book, he is a man that took a stand for what was right, and died for an innocent man. .
When you first meet Sidney in the book, he appears to be a lazy, self-loathing drunk, and all together the worst that society can put out. When you first meet him, he is sitting in a courtroom staring at the ceiling, unaffected by what is going on around him, and what is about to happen to him. "Mr. Carton's manner was so careless as to be almost insolent" (book the second chapter 3). As the conversation goes on, you see that Carton is very cynical and pessimistic.
As the book goes on, you see who Sidney Carton really is. He is not lazy as he seems, but he works very hard. Later on you learn that he wants to stop his alcoholism and reform his ways. He is nothing short of a genius. He is always taking in everything that takes place around him, and is very alert. He is not a man of virtues, but he does know right from wrong, and tries to do the right thing. He is still a despicable slob, despite all of this. He also considers life pointless and not worth the trouble it gives.
Sidney Carton's character really develops during the book. His big change is before Darnay and Lucie get married. He goes to see Lucie, and professes that the life he leads is not a good one, and a shame in God's eyes. He talks about how he doesn't think he can be better, only worse. Lucie tells him that he can always be a better man. His character changes greatly after that conversation. These changes affect the choice that Carton will make in the end. When Carton learns of Darnay's fate, Lucie asks Carton to help. Carton makes the decision to give his life so that Darnay could live. This is the unlikely hero that comes out in the end of the book. Carton is a changed man.
Sidney Carton is the most diverse character in The Tale of Two Cities.