The Rabbi isn't in the book very long before he succumbs to a heart attack, but he's a huge influence on the Golem and on us. So let's hang out with him for a bit, shall we?
At first, he's kind of creepy, dressed all in black and following the Golem around. But he turns out to be nice. When the Golem steals a knish (for a hungry child), the Rabbi pays for the meal and gives the Golem a place to stay. He names her Chava (after his grandmother), and he helps her find her passion for baking. And he doesn't stop there—he even gets her a job and finds her an apartment of her own. What a nice guy.
Then… things get dark for our holy man in black. He starts wondering if he should destroy the Golem. See, he made one before, albeit a teeny-tiny pocket golem, but he couldn't control it, and he's told that "all [golems] share the same essential nature" (8.43). If his Golem went all mini-smash-smash, what could a human golem do? Gulp.
The Rabbi starts doing some decidedly non-holy acts: stealing his friends' books to research the mysticism behind the golem, practicing some dark arts, and deciding to destroy a creature that may or may not have a soul. The man ends up compromising, creating a spell that will safely bind her to a new master, but that also requires her consent (so she's not stuck with some jerk), but by the time he finishes, he has worked himself to death. Literally. He has a heart attack and dies, but when the Golem finds his work, his spell lives on.