Gandalf

Thousands of years before Bilbo and Frodo, in the Second Age, a man falls from the sky inside a meteor. He's found by Nori Brandyfoot, a young Harfoot, from the people who came before the hobbits. He doesn't remember who he is, barely speaks their language and has a power he can't control. The Harfoots start calling him the Stranger.

At the end of season 1, three Mystics in white mistake him for Sauron. The Stranger stands up to them and learns he isn't: he's an Istar, and he's good. He heads off with Nori toward Rhûn.

In season 2, already in Rhûn, he drifts away from his friends and meets Tom Bombadil, who helps him understand his own power and tells him he has to find a staff. A Dark Wizard tries to win the Stranger over, and he refuses. The Dark Wizard destroys the canyon where the Stoors, another people of halflings, lived, and Nori and Poppy leave with them. The Stranger finds a staff in the canyon and realizes what he'll be called: Gandalf.

In the Third Age, Gandalf picks Bilbo Baggins as burglar for the company of Thorin Oakenshield, who wants to take Erebor back from the dragon Smaug. He marks the door of Bag End and sends thirteen dwarves there for dinner.

On the road, he saves the company from the trolls by splitting a rock and letting the sun turn them to stone. Radagast the Brown tells him something dark has taken Dol Guldur and hands over a Morgul blade. In Rivendell, Gandalf brings it to the White Council, with Elrond, Galadriel and Saruman, who brushes it off. Later he gets the company out of Goblin-town and calls the Eagles when Azog corners everyone in a burning forest.

At the edge of Mirkwood, Gandalf leaves the company. With Radagast, he visits the tombs of the Nine in the High Fells and finds them empty.

Alone in Dol Guldur, he faces the Necromancer and learns who he really is: Sauron, back again. The wizard loses the fight and ends up locked in a cage hanging in the fortress, watching an orc army march toward the Lonely Mountain.

Galadriel, Elrond and Saruman storm Dol Guldur, rescue Gandalf and drive Sauron out. Weak, the wizard hurries to Dale, at the foot of Erebor, to warn that an orc army is coming. Elves, men and dwarves nearly fight each other before Azog shows up.

In the battle, Gandalf runs the defense of Dale. Afterward he rides with Bilbo to the edge of the Shire and, as they part, makes it clear he knows about the ring the hobbit found in the goblin tunnels. He asks him not to use magic rings lightly. Bilbo pretends he has no idea what he's talking about.

Sixty years later, Gandalf rolls into the Shire in a cart full of fireworks for Bilbo's 111th birthday. He talks his friend into leaving the ring to Frodo and goes to Minas Tirith to read Isildur's scroll. He comes back, throws the ring into the fire and confirms it: it's the One Ring.

Saruman, whom Gandalf goes to see in Isengard, turns out to be on Sauron's side. The two duel, and Gandalf is trapped on top of Orthanc until an Eagle picks him up. In Rivendell, he joins the Fellowship of the Ring.

In Moria he hesitates, but leads the group through the mines. On the Bridge of Khazad-dûm he faces the Balrog, breaks the bridge and falls into the abyss with the demon, telling the others to run.

Gandalf comes back in Fangorn, dressed in white, and finds Aragorn, Legolas and Gimli. He tells them he fought the Balrog all the way to the mountain peak, died and was sent back. Now he is Gandalf the White.

In Edoras, he frees King Théoden from Saruman's control, which had been working through Gríma Wormtongue. Before the battle of Helm's Deep, he rides off on Shadowfax with a promise: at dawn on the fifth day, look to the east. He keeps it, arriving with Éomer's riders and turning the battle.

Pippin looks into Saruman's palantír and Sauron sees him. Gandalf takes the hobbit to Minas Tirith, where Denethor refuses to call for help. Pippin lights the beacons, and Rohan answers.

During the siege, Gandalf leads the city's defense, saves Faramir from the pyre his own father lit and comforts Pippin by describing death as a white shore. Then he marches to the Black Gate with Aragorn to distract Sauron. When the ring is destroyed, he flies an Eagle to Mount Doom and pulls Frodo and Sam out of the lava.

Years later, he sails from the Grey Havens with Frodo, Bilbo and the elves.

In The Hobbit, Tolkien barely explains where Gandalf goes when he drops out of the story; that's left to the appendices of The Lord of the Rings. And in the book The Lord of the Rings, he spends 17 years coming and going between Bilbo's party and Frodo's departure, a gap the movies shrink a lot.