Character Analysis
Big Love
Dumbledore and McGonagall are Harry's mentors and teachers. Ron and Hermione are Harry's friends. In between them sits a gigantic mass of hair and beard named Rubeus Hagrid: Hogwarts' groundskeeper and literal big man on campus.
Depending upon the exact moment, Hagrid can either be Harry's good buddy or his teacher, but he's always on Harry's side, and he'd rather die than let our hero down.
The mentoring stuff mostly happens in the early scenes. Hagrid is Harry's first introduction to the Wizarding World, and as such has to answer a lot of questions early on. It's a lot to take in, which is why Hagrid makes a better choice to explain it to him than Dumbledore.
Dumbledore's great, but he's not exactly the type you want to hang out with and throw back a few butter beers with. Hagrid is a little too much sometimes, since he clearly can't keep his mouth shut about important secrets, but his warmth and approachability makes him the ideal means to delivering basic information about this magical universe, including who and what Harry is.
When he first appears in that shack on the island where the Dursleys have gone to hide, Harry's about as miserable as he can get. And suddenly here comes this great beard with a man attached—he crashes through the door with two things Harry desperately needs: a friendly smile and a little information on why he has freaky powers.
HAGRID: Did you ever make anything happen? Anything you couldn't explain when you were angry or scared?
Why, yes, Hagrid. As a matter of fact, Harry can talk to freakin' snakes. How did you know?
Big Mouth
Hagrid's friendliness as a mentor and information tool means he segues quite easily from being a teacher to a friend. Once he's eased Harry and his friends into Hogwarts, he can leave the stern lessons and scary warnings to them, and just be there for Harry.
Again, he has a hard time keeping his yap shut (making it easy for Harry and his pals to pump him for information), but he seems quite cheerful about it, and the familial way he lets Harry and the gang just chillax in his hut means that he has no hard feelings about it.
Even when he screws up and gives away more information than he should, there's no hostility or anger. He just quietly berates himself and keeps chatting with the kids. His usual refrain goes something like this…
HAGRID: I shouldn't have said that. I should NOT have said that…
Thanks for being a blabber-mouth, Hagrid. (No really, we're glad. He keeps us in the loop, too.)
Lesson Learned
Hagrid's general Santa Claus tendencies are hidden behind a very imposing exterior. When he first kicks down the door to collect Harry, he really looks like a giant out of a fairy tale—you know, the kind that says things like "I'll grind your bones to make my bread"—and it's only when he gives out a disarming "sorry about that" that we realize he's not a threat.
In fact, this sums up Hagrid's greatest lesson: things aren't always what they appear to be in the Wizarding World. Turbans can hide evil wizard faces. Mirrors can reveal hidden desires. And massive giants with booming voices can turn out to be sweeter and milder than baby lambs.