Batman: Two Face
The relationship between Batman/Bruce Wayne and Harvey Dent was done perfectly in "The Dark Knight" as it showed how Gotham viewed them both. Batman was clearly the Dark Knight of Gotham due to the fact that some feared him while some loved him. Harvey Dent as the star district attorney was the face of change in Gotham, and everyone loved him. Even more so, he was one of Batman's closest allies. However, when the dark underbelly of the city turned him due to a horrible accident he became Two Face. As Two Face, he was still Harvey on one side and the other he was a hideous monster that embody everything that Gotham is, like being ugly and atrocious. His normal face that was unaffected by the accident is a constant reminder to the city and to Batman, that even the incorruptible can be turned by the darkness within Gotham. Sal Maroni attacked him by throwing acid in his face in a court room, permanently disfiguring his face and in turn fracturing his mental state. Two Face was a schizoid criminal mastermind who had an obsession with the number two, much likely due to the duality within himself.
Harvey Dent's childhood consisted of hardship, so much so that he grew bitter to the upper class. His family was in the lower class and due to his harsh surroundings he had developed repressed mental illnesses of his own, such as schizophrenia and a bipolar disorder. However, as he grew up he had a great work ethic and worked hard. That served him well as he would become Gotham's district attorney, and a very good one. He earned the nickname "Apollo" by the media due to the fact that he was charming, good looking, and seemingly untouchable. He dedicated himself to upholding law and order which then led to him becoming one of Batman's allies and the two would even become friends. When he was a district attorney, the biggest criminal threat present in Gotham was the crime boss Sal Maroni. Dent would create an alliance with Batman and Commisioner Gordon in hopes of bringing down the mafia within Gotham but his angrier temperament led to the two to develop a slight distrust for him. So much so that Batman and Gordon wondered if Dent was indeed the vigilante dubbed "Holiday." The alliance ultimately came to an end when Maroni, during a trial, threw acid in his face. Maroni had reason to believe that Dent was responsible for the death of his father, although Dent didn't do it. Dent was left horribly scarred on his face and his left hand. He was admitted into a hospital as soon as possible, but the pain was not only physical but also mentally. Dent escaped from the hospital and quickly descended into madness. He would become obsessed with duality and opposites to the point that he even developed a villainous second persona nicknamed Two Face. Two Face was the complete opposite from the law and order persona of Dent. His obsession with duality even appeared in his clothes, which usually composed of two halves that consist of opposing material. At all times he would even carry a double sided coin with one side scarred, which he constantly would flip to make decisions. Frequently, he would flip the coin to decide whether or not someone should live or die. The scarred side of the coin would lead to him committing a crime, while the clean side would allow him to do the right thing.
Early in his career as the villainous Two Face, he would have frequent run ins with his former ally Batman. Two Face had attempted to cut all ties with his past wife, including his lovely wife Gilda. This, however, proved to difficult for the good that was left inside of him. He began to visit Gilda, claiming that he had regained his normal face with the help of plastic surgery. Gilda realized quickly that the man she had once loved was different and chastised him for it. Eventually he would be apprehended by Batman, with the help of his new sidekick, Robin. Dent had plastic surgery performed on his face by a one, Dr. Ekhart (it is okay to laugh), and the doctor seemingly repaired Dent's face for good. The facial reconstruction seemed to help his fractured mind, but Ekhart's assistant placed suspicion on him once more by disguising himself as Two Face and committing crimes. Batman, however, was able to see through the disguise and helped in clearing Two Face's name. For the next two years, he was able to live a normal life until an actor by the name of Paul Sloane was scarred in a similar fashion. Sloane also had a psychotic break following the event and began to believe that he was in fact Two Face. In his delusion, he ended up getting arrested by Batman for several attempted robberies and eventually had his face recovered the same way Dent did. Dent's good fortunate would not last long as eventually he would be caught in another tragedy. This time around he was caught in an explosion that scarred his face once again. The ordeal drove him to madness once again, and he even sought out Paul Sloane to make him go through it all again. Sloane eventually would be rescued by Batman, and Dent would be jailed for his crimes. On the other side of prison bars this time, Dent's psychosis seemed much more permanent following his tragedy.
In the aftermath of the earthquake that left Gotham in shambles, Two Face was able to escape custody and quickly found his way to Commissioner Gordon. He placed Gordon on trial for his actions during the story line "No Man's Land." Two Face made himself present as the judge and the executioner for Gordon's faux trial. Gordon played upon Two Face's duality to demand Harvey Dent to help him as his defense attorney. Dent cross-examined Two Face, which won an acquittal of Gordon. Shortly after, he would meet Gotham City Police Department detective Renee Montoya who was able to connect with the softer side of the beast. Renee was kind to him to the point that Two Face began to love her. However, the romance was very one-sided. Upon realizing he was not as loved as he wanted, he ousted Renee as a lesbian and framed her for murder. In his delusion, he figured that if he took away everything from her then she would be left with no choice but to be with him. Instead, it made Renee furious and the two fought. Eventually a gun was drawn and the two fought for control over it. Batman intervened as a good hero always does and locked Two Face upon once again in Arkham Asylum. A short time later however he met Dr. Thomas Elliot. Elliot happened to be a brilliant neurosurgeon and attempted to help Two Face regain his sanity. Two Face indeed regained his sanity as Harvey Dent, and his evil persona seemed to be gone forever. However, Batman stories are really like a story book ending as Elliot turned out to be the villain known as Hush. Hush had hoped that he could use Dent as a pawn in a scheme to bring down Batman. Dent, with renewed sanity, stood by the side of law and order and betrayed Hush catching him in time where he in fact saved Batman's life. Dent shot and killed Hush.