Character Clues
Character Analysis
Direct Characterization
2001 doesn't do complex characterization in any sense. The characters are mostly there so Clarke can describe the cool future stuff that happens to them. As a result, the most common form of characterization in the novel is just directly telling you what the characters are like, or are supposed to be like.
When Clarke wants you to know that Moon-Watcher is a genius, he doesn't fool around, he just writes:
Then, not for the first or last time, he proved himself a genius. (4.16)
When he wants you to know that Hal is afraid of being disconnected, he just says:
To Hal, this was the equivalent of Death. For he had never slept, and therefore he did not know that one could wake again… (27.9)
Direct characterization: For a novel not very interested in characterization, it's the easiest way to get the job done.
Speech and Dialogue
The one really inspired piece of characterization in the novel is Hal's dialogue. His friendly chatter with Dave has an eerily bland homicidal ring that has become justly famous (from both the movie and the novel):
I don't want to insist on it, Dave, but I am incapable of making an error. (24.23)
And:
You know that I have the greatest possible enthusiasm for this mission. (24.43)
It's mostly through dialogue that Hal comes across as the world's most terrifying cubicle worker. And you thought your laptop was being a pain when it took forever to load that YouTube vid.
Actions
The novel will sometimes use actions as a way to provide simple characterization. Much of this is just a matter of showing that Bowman, Poole, Floyd, and other professional space type people are professional and competent:
Frank Poole had been through the whole routine before, but he took nothing for granted… (25.1)
That tells you that Poole is methodical and careful and competent. Most folks the novel shows you are careful and methodical and competent. Only Hal is neurotic—which is why Hal is the only one who's any fun to be around.