You can see the "hero" in 2001 as the human race itself. From that perspective, the call to the journey here is issued by the slab, which drops down to earth to tell the man-apes that if they want to escape hunger and dread, they need to start evolving. It's a long, lonely road up the evolutionary ladder, but some man-ape has to do it.
Humans set out to be intelligent…and then set out farther to fly to the moon…and then set out farther to go to Saturn, where a homicidal computer ambushes them. Stupid journey.
Arrival and Frustration
The human race (in the person of boring David Bowman) gets to the Star Gate, which is where the aliens pointed the man-apes all those years ago.
Through the Star Gate, there's lots of mind-blowing stuff. Psychedelic colors, awesome suns, magical fake apartments. Who would have thought a man-ape would get this far?
Uber-evolved space-babyhood is achieved! That was the goal all along, as it turns out. Triumph of the slab and the space baby, at long last.