The answer is g.

Congratulations to RJWhite, who, although he is confused as to the character's name, correctly identifies the protagonist of 2001 as "whomever was trying to propel the human race forward."

2001 is, essentially, an education drama, not unlike Blackboard Jungle or Dangerous Minds.  There is a  wise teacher who has been put in charge of a bunch of wild students in the inner city, with their gang wars and primitive ways, and the teacher must show them the beauty of learning and betterment while hoping they don't use their new intelligence to kill each other.  Kubrick's bold stroke was to make an education drama where the "wise teacher" goes unseen.  If you can imagine Stand and Deliver with a big black slab instead of Edward James Olmos, that's pretty much 2001.

"Humanity" is, in fact, the antagonist of 2001.  The protagonist is trying to teach them, and while humanity is capable of learning, their "background" continues to "keep them down."  The drama of 2001 is, "can the protagonist change the antagonist, given that the antagonist is probably evil to its core?"

"Dave" is indeed a "main character," but his story is, basically, a subplot.  Dave is the student who advances to the State Finals and must "prove himself."  The movie, essentially, ends when the student walks out onto the stage to prove what he's learned, how far he's come -- but then doesn't show us the speech.

Eronanke supplies a mind-blowing answer to a mind-blowing movie and suggests that "destiny" is the protagonist, which is an intriguing idea, if "destiny" is indeed what the movie is about -- which I don't think it is.  But I also think that "destiny" is no kind of protagonist to hang a 2-hour, 20-minute movie on -- even if that movie's prime directive is to blow one's mind.

Mr. Noy correctly identifies the four large-scale story chunks that give the movie its shape.  I'm going to go ahead and call these chunks the acts of the movie, even though they don't really function as acts in the traditional sense.  This is typical of Kubrick's approach to story structure -- three or four very long sequences instead of three acts made up of short scenes -- and is, to me, the thing that makes AI such an odd movie-watching experience; Spielberg made Kubrick's script his own, but kept the decidedly Kubrickian structure.

Here is the plot of 2001, as told from the protagonist's point of view.
_____

ACT I

There is this bunch of extraterrestrials.  They have a machine that makes creatures smarter.  Let's call them the Invisible Extraterrestrials (the IET).

They spot Earth.  Earth has relatively intelligent creatures on it called apes.  The apes are doing okay but they're eating vegetables and living in caves and getting into fights over resources (plus ca change).  The IET, for reasons unknown, decide to help the apes along in their evolution.

They uncrate three of their smart-making-machines -- small, medium and large.  They leave the small one on the planet Earth, in the middle of the ape community, they bury the medium-sized one beneath the surface of the moon, and they put the large one out in space, somewhere near Jupiter.

The scene we don't see is the IET discussing their plan: "So, we'll put the small one in the middle of the ape community, and the machine will do its thing, and the creatures will either become smart or they won't.  If they do become smart, we know that they'll eventually fly to their moon and discover the one we bury there.  We'll stick a light-sensitive device in the second one, so that when it gets hit by sunlight it will send a radio signal to the big one next to Jupiter, and if the creatures are smart enough to make it to the big one, then we'll give them all the intelligence in the universe, and if that doesn't totally blow their minds, they will evolve to the next step."

So they leave the small monolith in the middle of Apetown.  The apes wake up in the morning and see the monolith.  Moon-Watcher (the lead ape) touches the monolith, the monolith does its thing, makes Moon-Watcher a little bit smarter, and the first thing Moon-Watcher does with his new intelligence is to pick up a bone and beat his enemy to death and use his new intelligence to stop eating vegetables and start eating meat.

So, here we have the central conflict of 2001 -- the protagonist (the IET) want to make humans intelligent, but humanity (the antagonist) has this thing where their nature is, at its root, homicidal.  The question of the movie, which is left unanswered, is "can people evolve to the point where they don't kill each other any more?"

(The novel, in my opinion, answers "no," but that is not the concern of this journal.)

But that's it -- that's the whole movie.  There's a bunch of invisible extraterrestrials who want to educate humanity but humanity may just be too homicidal to survive the process.

(Each one of the four acts dramatize this central conflict in different ways.  In Act I, we see that an ape, given a little intelligence, kills another ape.  In Act II, we see that humanity, given a few million years of evolution, has advanced to the point where they can destroy all life on the planet with atom bombs and every bit of human interaction must be rife with suspicion, secrecy and coded language.  In Act III, we see that humanity has gotten smart enough to create a machine capable of killing people on its own, and in Act IV we see that a man, even after gaining all the knowledge in the world, still has to eat and still spills his wine.  So the answer to the question "what happens after the end of the movie," it seems to me, is a very pessimistic one -- and indeed, Kubrick once said that he wanted to end the movie with a scene showing the world destroyed by atom bombs but decided it was too much like the ending of Dr. Strangelove.)


ACT II

It's the year 2001 or thereabouts (the rest of the movie covers an 18-month time-span, so obviously the whole movie doesn't take place in 2001).  Dr. Floyd goes to the moon.  And we see how sophisticated people have become, and how boring -- they glide across the surface of the moon and can talk about nothing but what kind of sandwiches they have.  (Intelligence and food again, stuck together.  No matter how smart you get, you still have to eat, and something still has to die for that to happen.)

And there's a bunch of hugger-mugger about "The Russians" and so forth, but the whole act is basically a bunch of "plot" about uncovering the second monolith and getting it exposed to the sunlight -- once that happens, the act ends abruptly and we never hear about any of those people again.


ACT III

A lovely subplot on the spaceship Discovery about Dave and Frank and the frozen astronauts and the murderous computer.  There are more scenes with food, and more scenes showing how, no matter how intelligent humans get, no matter how bloodless and dispassionate, they are still animals who eat and piss and shit and sweat.  HAL 9000 doesn't have those problems, of course (and here Kubrick points toward AI -- machines as the final evolution of humanity) -- he is more bloodless and dispassionate than any of the humans on board, although we find that that only enables him to kill more bloodlessly and dispassionately, leading to Dave having to take matters into his own hands and kill HAL.

At the end of Act III, just after Dave kills HAL, the video comes on and Some Guy on the video tells us the story of the movie.  The scene comes after so many mind-blowing visuals one is forgiven for missing it, but the guy on the video actually takes a few minutes to sit there quietly and patiently explain the plot of the whole movie to us.


ACT IV

Dave takes his pod to go investigate the extra-large monolith out in space.  His encounter with the monolith gives him all the intelligence in the universe (that's the big famous mind-blowing psychedelic freakout scene), but he's still human.  He still has to eat and his body will still decay.

That's okay, as it turns out.  The IET give Dave a place to relax and grow old.  The scene where Dave "sees himself" getting old is a misdirect -- all that's happening is that Dave is growing old, over a period of years, and Kubrick is trying to think of an interesting way to shoot that bit of exposition.  The fact that the inside of the monolith looks like some kind of postmodern French hotel suite is just the IET's way of trying to think of something to make Dave comfortable while he grows old and dies.

Finally Dave dies and, because he's obtained all the intelligence in the universe, he is reincarnated as the "Star-Child," the big green fetus who is seen approaching the Earth at the end of the movie.

Now that the IET have given humanity all the knowledge in the universe, what will humanity do?  Will the Star-Child do good works and teach the world to sing, or will it use its super-intelligence to wipe out all of humanity?  That is, will the protagonist's goal be reached or will it be frustrated by the antagonist's inherent self-destructiveness?

(This, of course, assumes that the protagonist's goal is for humanity to better itself.  For all I know, the IET's goal is to get us to wipe ourselves out so they could come and steal all our resources.  That would make the monolith not an intelligence-generating machine but a homicide-generating machine.)