Stranger in a Strange Land
Ah, the exposition guru. Seriously, whenever you need someone with the information to move the story along. Ben's your man. Without him, we'd have no idea what on Earth (ahem, on Mars) happened that led to Mike's Martian upbringing (check out all of Chapter 4 for some examples).
Ben uses his column in the newspaper to promote freedom, particularly freedom from oppressive government tactics and rules. He has a particular bone to pick with Douglas, whom he views as his opposition. Also, Douglas's people did try to have Ben wiped clean off the grid. So, there's that.
Later in the novel, Ben visits Mike's Church of All Worlds. And boy is he in for a surprise: "Patricia Paiwonski gave Ben Caxton the all-out kiss of brotherhood before he knew what hit him" (31.1). Our exposition guru definitely didn't see that one coming. Still, his jealousy over seeing and thinking about other people loving on and making love to Jill (whom he desires in a not-so-secretively kind of way) causes him to panic and flee the church.
Then it's right back to being exposition guru, keeping Jubal up to date in Part 5. Well, it's a plot-heavy job, but someone has to do it.