Gandalf

Gandalf the Grey was a wizard sent to Middle-earth to help the Free Peoples battle the Dark Lord Sauron, while also being part of the Fellowship of the Ring.

Bilbo's birthday
Gandalf the Grey was present at the birthday of his old friend Bilbo Baggins and saw when he used the One Ring to become invisible in order to leave the Shire without hurting the feelings of his nephew Frodo Baggins.

One Ring to rule them all
He came to Frodo after some time in order to both check on him and tell more about the Ring that Bilbo gave to him. He revealed that it was forged by Sauron in Mount Doom to controll all other Rings of Power, thus ruling every race on Arda. Gandalf warned the hobbit that the Great Enemy knew of his prize's location and urged him to go with Sam and his cousins Merry and Pippin away from the Shire and meet with him in Bree at the Prancing Pony inn.

Saruman's changing of sides
He then left for Isengard to meet with his comrade Saruman. He told him of the growing threat from Mordor, but was shocked to see his old friend unmoved by the news. This prompted Saruman to reveal the alliance between him and Sauron, his plan to gain the One Ring for himself and his abandoning of the title of White in favour of Saruman of Many Colours. The traitor imprisoned Gandalf in the Tower of Orthanc. He was rescued by a Great Eagle and brought to the Hidden Vale.

The Council of Elrond
He was in part responsible for the magical flood that stopped the Nine Nazgûl from reaching the wounded Frodo Baggins and helped him recover with aid from Lord Elrond. In Rivendell, they organized a council of Men, Elves, Dwarves, Hobbits and Wizards. Ultimately Frodo chose to be the one to take the Ring into Mordor and cast it in the fires from where it came and a group of nine companions amongst them being Gandalf himself was selected to follow and protect him.

The Pass of Caradhras
During their journey through Caradhras, the Fellowship of the Ring settled that they would go through the mines of Moria.