Rand's stated goal in writing fiction was to portray her vision of an ideal man. The character of Howard Roark, the protagonist of The Fountainhead, was the first instance where she believed she had achieved this. Roark embodies Rand's egoistic moral ideals, especially the virtues of independence and integrity.
The character of Roark was at least partly inspired by American architect Frank Lloyd Wright. Rand described the inspiration as limited to specific ideas he had about architecture and "the pattern of his career". She denied that Wright had anything to do with the philosophy expressed by Roark or the events of the plot. Rand's denials have not stopped commentators from claiming stronger connections between Wright and Roark. Wright equivocated about whether he thought Roark was based on him, sometimes implying that he did, at other times denying it. Wright biographer Ada Louise Huxtable described significant differences between Wright's philosophy and Rand's, and quoted him declaring, "I deny the paternity and refuse to marry the mother." Architecture critic Martin Filler said that Roark resembles the Swiss-French modernist architect Le Corbusier more closely than Wright.
In contrast to the individualistic Roark, Peter Keating is a conformist who bases his choices on what others want. Introduced to the reader as Roark's classmate in architecture school, Keating does not really want to be an architect. He loves painting, but his mother steers him toward architecture instead. In this as in all his decisions, Keating does what others expect rather than follow his personal interests. He becomes a social climber, focused on improving his career and social standing using a combination of personal manipulation and conformity to popular styles. He follows a similar path in his private life: he chooses a loveless marriage to Dominique instead of marrying the woman he loves—who lacks Dominique's beauty and social connections. By middle age, Keating's career is in decline and he is unhappy with his path, but it is too late for him to change.
Rand did not use a specific architect as a model for Keating. Her inspiration for the character came from a neighbor she knew while working in Hollywood in the early 1930s. Rand asked this young woman to explain her goals in life. The woman's response was focused on social comparisons: the neighbor wanted her material possessions and social standing to equal or exceed those of other people. Rand created Keating as an archetype of this motivation, which she saw as the opposite of self-interest.
Dominique Francon is the heroine of The Fountainhead, described by Rand as "the woman for a man like Howard Roark". Rand described Dominique as similar to herself "in a bad mood". For most of the novel, the character operates from what Rand viewed as wrong ideas. Believing that the values she admires cannot survive in the real world, she chooses to turn away from them so that the world cannot harm her. Only at the end of the novel does she accept that she can be happy and survive.
The character has provoked varied reactions from commentators. Philosopher Chris Matthew Sciabarra called her "one of the more bizarre characters in the novel". Literature scholar Mimi Reisel Gladstein called her "an interesting case study in perverseness". Writer Tore Boeckmann described her as a character with conflicting beliefs and saw her actions as a logical representation of how those conflicts might play out.
Gail Wynand is a wealthy newspaper mogul who rose from a destitute childhood in the ghettoes of New York to control much of the city's print media. While Wynand shares many of the character qualities of Roark, his success is dependent upon his ability to pander to public opinion. Rand presents this as a tragic flaw that eventually leads to his downfall. In her journals Rand described Wynand as "the man who could have been" a heroic individualist, contrasting him to Roark, "the man who can be and is". Some elements of Wynand's character were inspired by real-life newspaper tycoon William Randolph Hearst, including Hearst's yellow journalism and mixed success in attempts to gain political influence. Wynand ultimately fails in his attempts to wield power, losing his newspaper, his wife, and his friendship with Roark. The character has been interpreted as a representation of the master morality described by philosopher Friedrich Nietzsche; his tragic nature illustrates Rand's rejection of Nietzsche's philosophy. In Rand's view, a person like Wynand, who seeks power over others, is as much a "second-hander" as a conformist such as Keating.
Ellsworth Monkton Toohey is Roark's antagonist. He is Rand's personification of evil—the most active and self-aware villain in any of her novels. Toohey is a socialist, and represents the spirit of collectivism more generally. He styles himself as representative of the will of the masses, but his actual desire is for power over others. He controls individual victims by destroying their sense of self-worth, and seeks broader power (over "the world", as he declares to Keating in a moment of candor) by promoting the ideals of ethical altruism and a rigorous egalitarianism that treats all people and achievements as equally valuable. Rand used her memory of the British democratic socialist Harold Laski to help her imagine what Toohey would do in a given situation. She attended a New York lecture by Laski as part of gathering material for the novel, following which she changed the physical appearance of the character to be similar to that of Laski. New York intellectuals Lewis Mumford and Clifton Fadiman also helped inspire the character.