The characters in this book can be divided into two camps: those who do things and those who don't. The people involved in Galt's strike are definitely doers. They are linked to themes of movement, of choice and decisions, and to a variety of "active" professions, such as transportation industries. The strikers are particularly characterized by the decisions they make, which lead them to take decisive actions, such as building the John Galt Line in Dagny's case or joining the strike in Ellis Wyatt's case. The looters are shown to be indecisive and prone to panic. They tend to appear in scenes where they are gathered together in small rooms, sitting still and avoiding making decisions.
Given how central work is to Galt's philosophy, it makes sense that occupation would be a major source of characterization in this book. All of the people affiliated with Galt are defined as hard workers who perform their jobs exceptionally well. Some of these characters are linked to highly symbolic professions: for instance, the sturdy and collected Henry Rearden produces steel. Other professions represented here are notable for being vital to the country and to the book's broader themes. For example, we meet lots of people involved in various transportation professions (Dagny with the railroad, Lawrence Hammond with his cars, Dwight Sanders with his airplanes). Transportation is of course vital to the country's survival and it is also tied in with the importance of motion in Galt's philosophy. By being involved in these professions, these characters become important emblems of Galt's strike and go on to play important roles in the strike and in Atlantis.
Galt's Atlantis could be a gigantic J. Crew ad, given how "really, really ridiculously good looking" (Zoolander shout out) everyone there is. This isn't just some sort of convenient trope, though, where good people are attractive and bad people are ugly. Galt's philosophy emphasizes the connections between people's minds and bodies; good morals are reflected in one's outer appearance. The looters, for their part, are frequently some combination of weak and mean looking, which reflects their inner selves. The thug-like Cuffy Meigs sports a crew-cut and resembles a bouncer. And the indecisive and whiny James is described as flabby and as having bad posture; he is spineless in a literal and a figurative sense.
The types of romantic and/or sexual relationships that characters have in the novel are a vital clue to their characters. We included an "and/or" above because the good characters associate sex with love, while the bad characters have sex for rather unromantic, immoral reasons: petty revenge (Lillian and James), manipulation and control (James and Cherryl), just for the heck of it (James and Betty Pope). The way people speak about sex also does a lot to characterize them. Francisco sees sex as an expression of people's values and thinks it's a good thing. The rotten Mayor Bascom discusses Hank and Dagny's relationship like it's tawdry and shameful. What and who people love also provides a lot of insight into their characters, since love reflects people's values and inner selves here.
People really love speechifying in this book, so what they say plays a major role in establishing who they are as characters. But how people speak also provides us with a lot of great characterization. It's important that the people associated with Galt tend to speak in similar styles, while the looter crowd speaks in a very different way. Galt and friends (sounds like a bad sitcom) are articulate, truthful, and very blunt. They discuss facts and ideas clearly and pointedly. The looters, meanwhile, are vague and manipulative; they often say one thing but mean something very different. When the two groups come together, the looters often come off as confused, while the strikers are often very terse and blunt. Here's a quick example:
The man leaned back, looked at Rearden incredulously and asked "What are you after?"
"I? What do you mean?"
"You're in business to make money, aren't you?"
"You want to make a big a profit as possible, don't you?"
"Then why do you want to struggle for years...rather than accept a fortune for Rearden Metal? Why?"
"Because it's mine. Do you understand the word?"
The man sighed and rose to his feet. (18.104.22.168-76)
Dialogue in this book doesn't characterize individual characters so much as it helps to demonstrate which groups the characters belong to, and what philosophies those groups support.
This method of characterization is pretty obvious, given that this book is largely about philosophy. In fact, Galt's philosophy itself believes that a person is defined by his or her opinions and the actions that result from those opinions. As with speech and dialogue, thoughts and opinions are often used to indicate which philosophy a character supports rather than anything uniquely individual about them. However, a lot of characters' inner and expressed thoughts help to give us insight into their problems, their concerns, and their goals. For instance, Dagny often thinks about finding the one man she can love, which plays a major role in focusing her values and defining who she is. Hank, meanwhile, is concerned with morals relating to sex and love, helping us to better understand the conflicts he has with his family and his own guilt.