Most of the characters in Brave New World are static and flat: they are undeveloped and do not change because they are born into and conditioned to be in a caste system. This is especially true of the female characters, Lenina and Linda, who are superficial, addicted to pleasure, and have no real sense of identity or femininity. It is also true of the Director, Mustapha Mond, and Henry Foster, all of whom seek to protect their positions at the top of the caste system.
The only two characters who change and are self-aware are Bernard and John. Whereas Bernard rebels against the values of the "utopia" at the beginning, John rebels against them at the end of the novel. As the novel progresses, the two switch roles: Bernard loses his courage to rebel, and John succumbs to the pleasures of "orgy-porgy." Knowing that he is forever lost in this new world, John kills himself--becoming a kind of tragic-comic hero. Of course, Huxley exaggerates all the behaviors of his characters in order to show the effects of government mandated birth control, unbridled mass media, addiction to drugs and pleasure, and the remediation of books as the basis for education.