He was portrayed by the late Brad Renfro in the film.
A teenage sociopath who takes pleasure from hurting and torturing animals, Todd is fascinated by the Holocaust and other Nazi crimes (and just Nazism in general), Todd also aspires to behave as a nazi, and after discovering that his elderly neighbor "Arthur Denker" is in reality former nazi Officer Kurt Dussander, blackmails him into telling him about life as a Nazi during the Holocaust. Callous and violent, Todd is also violently anti-semitic and often fantasizes about raping Jewish women.
Despite his vicious fantasms, Todd actually prefers murdering over torturing and has no qualms killing anyone in the most brutal ways possible. A proud social darwinist, Todd believes that homeless people are useless and failures, and as such deserves to be murdered.
At the end of the novel, Todd loses his mind and began killing anyone in a five-hours killing spree on the highway, revealing that he is not only a racist, but also a misanthrope as well with no concerns over anyone.
The book opens in 1974, with Todd Bowden confronting his neighbor Arthur Denker and revealing that he knows of his past as a Nazi war criminal. He then blackmails the old Nazi into telling him detailed stories of his war crimes and part in the Holocaust, also buying him a Nazi SS uniform that he forces the old man to wear. For Todd is darkly fascinated by the Holocaust and of Nazism in general, and takes great joy in ordering Dussander around and forcing him to do what he wants.
However, as the months go by and Todd spends more and more time with Dussander indulging himself, his grades in school steadily slip. Dussander goes to meet with Todd's guidance counselor disguised as the man's grandfather, fooling said guidance counselor and promising to improve Todd's academic performance. He blackmails Todd into going along with it, as Dussander wishes for Todd to actually succeed academically. Todd thus steadily improves his grades under Dussander's guidance, but also decides that the doesn't need Dussander anymore and so secretly plans to kill him and make it look like an accident.
Over the next few months, Todd (and Dussander), murder homeless people, and Todd for his part also loses his virginity, but finds sex unsatisfying compared to murder, from this concluding that his girlfriend's being Jewish is the reason for his sexual impotence. When he is no longer able to keep up his murders of homeless people, he takes to shooting at passing cars from a concealed spot overlooking a freeway. Later, when Dussander has a heart attack burying the body of one of his murder victims, he summons Todd to help him, and Todd does so (having earlier believed that Dussander had dirt on him when the old man was in fact bluffing). Dussander is hospitalized, admits to Todd that he was bluffing, and tells him not to see him again (and also warns him to not get careless where his murders are concerned).
After Dussander commits suicide and is outed as the Nazi war criminal that he was, Todd manages to convince his parents that he did not know about Dussander's true nature, but the police detective Richler and Nazi hunter Weiskopf are not as convinced when they question him. Worse for Todd, a vagrant recognizes him as the last person who was seen with several of the murdered homeless people, and tells the police as much. Similarly, the guidance counselor from before meets Todd's real grandfather and similarly realizes that he has been duped. He confronts Todd, who violently murders him, takes his rifle and ammunition to his hideout by the freeway, and goes on a shooting spree that ends with his death at the hands of the police five hours later.
In the movie, the overall story is the same, save that most of the murders are cut, as are Todd's fantasizing raping various young women and girls. However, Todd also manages to avoid facing any consequences for his crimes by blackmailing his guidance counselor into keeping quiet about what he has learned.