Gandalf knows the corrupting power of the Ring. He doesn't even trust himself with it. But knowing Frodo's pure heart, he enlists the Hobbit to help him deliver the Ring to Rivendell.

Before his fall, Saruman was the chief of both the wizards and of the White Council. However, his deep study of the Rings of Power and Sauron's other magic corrupted him. He betrays Gandalf and imprisons him atop the tower of Orthanc.

MERRY: I don't know why he's so upset. It's only a couple of carrots.
PIPPIN: And some cabbages. And then those three bags of potatoes that we lifted last week. And then the mushrooms the week before.

They were once men. Great kings of men. Then Sauron the Deceiver gave them nine rings of power. Blinded by their greed, they took them without question, one by one, falling into darkness. And now they are slaves to his will. They are the Nazgûl. Ringwraiths. Neither living or dead.

When Frodo arrives at the Inn of the Prancing Pony, Gandalf is nowhere to be found. The proprietor says he hasn't been around for six months. Fortunately, Aragorn ("Strider") is there to watch out for the Hobbits.

Strider fights off the Nazgûl, but Frodo is wounded by one of the wraiths who stabs him with a Morgul blade, which will cause him to turn into a wraith if he does not receive the proper care. While chased by the Nazgûl, Frodo is carried by the Elf Arwen to the Elven haven of Rivendell, and healed by her father, Elrond.

Gandalf communicates with a small moth, which alerts Gwaihir the Windlord, lord of the Great Eagles, who rescues Gandalf from the top of the tower.

ELROND: The time of the Elves is over. My people are leaving these shores. Who will you look to when we've gone? The Dwarves? They hide in their mountains, seeking riches. They care nothing for the troubles of others.
GANDALF: It is in Men that we must place our hopes.
ELROND: Men. Men are weak.... It is because of Men that the Ring survives.

Aragorn is a great ranger and warrior, and as Isildur's heir, he is crowned the first High King of Gondor and Arnor since the short reign of Isildur.

Those present at the Council of Elrond represent the three largest races of good in Middle-earth: Men, Elves, and Dwarves.