Disaster and misery
Unlike the utopia, which tends to describe a better or ideal world, dystopia ("dys"=bad) is a story set in the future with a negative outcome. It often describes the end-time state of a fictional society and shows how the society eventually perishes. The partial destruction of society in Fahrenheit 451 is caused by the nuclear war that wipes out the megacity at the end of the novel.
A character typical of dystopias is a hero who fights against the system. In Fahrenheit 451, the conformist main character Guy Montag doubts the system for the first time after he meets his young neighbor. He no longer wants to continue working as a fireman. By possessing banned books, he makes himself liable to prosecution, and this sets the plot in motion.
Guy's superior, the intellectual but system-loyal Captain Beatty seems to be a particularly strong villain and adversary, but in reality, he too suffers from the terrible tyranny of the majority. Guy kills Beatty and escapes to the countryside, where he plans to continue his fight for a better future.
Totalitarian systems are typical forms...