Harry Potter and the Deathly Hallows
Affiliation: Order of the Phoenix
Professor: Care of Magical Creatures
Always Harry's friend and protector, Hagrid enters Deathly Hallows on Sirius's old flying motorbike to carry Harry safely to the Burrow. (This scene nicely echoes the opening chapter of Harry Potter and the Half-Blood Prince, when Hagrid carries baby Harry on Sirius's bike to the Dursleys to be raised. And we bet that clever Rowling did this on purpose.) Though other members of the Order of the Phoenix are carrying decoy Harrys (Ron, Hermione, Fleur, and others disguised as Harry, with the help of Polyjuice potion), it's Hagrid who's entrusted with protecting the real Harry. Now that's big.
From the time that Book 6 was released until Book 7 came out, fans were terrified that Hagrid would die. Even Rowling's sister was worried, and said "If Hagrid dies, I will never forgive you" (source). Rowling seems to play upon all of our fears in Chapter 4, which closes with Hagrid apparently plummeting to his death, and the title of Chapter 5 – "Fallen Warrior" – which actually refers to Mad-Eye Moody. (She still had us scared.)
Interestingly, though, we were all working ourselves up for nothing. Since she began the series, Rowling has always intended for Hagrid to survive and carry the seemingly dead Harry out of the woods after Harry sacrifices himself:
It was very significant […] Hagrid brings Harry from the Dursleys. He takes him into the wizarding world … He was sort of his guardian and his guide ... And now I wanted Hagrid to be the one to lead Harry out of the forest. (source)
Hagrid has always played a key role in Harry's life, and continues to do so in Deathly Hallows. In the Epilogue we find that Hagrid is still at Hogwarts, as little Al Potter will be meeting him for tea.