What is Gandalf's origin story?

Well, first off, Gandalf being a Maiar is a huge part of his origin. It gives him his power and wisdom. Then, the fact that he was sent to Middle - earth by the Valar is also crucial. This mission from the Valar shaped his role in Middle - earth. He was part of a group of Istari, and this also stems from his origin story as he was chosen for this role because of his nature as a Maiar.

The fact that Gandalf is from the Ainur is a very important part of his origin story. Also, his transformation into the form of an old man is significant. It allowed him to interact more easily with the races of Middle - earth, like humans, dwarves, and elves. And of course, his being sent to oppose Sauron is a central aspect of his origin. It shaped his entire journey in Middle - earth.

His being a Maia and sent by the Valar.

Gandalf is a Maia. He was sent to Middle - earth by the Valar. He was one of the Istari, a group of wizards. His purpose was to guide and oppose the rising power of Sauron.

Well, Gandalf is from the Ainur. He was among those Maiar who were sent to Middle - earth. His purpose was mainly to help the good against the forces of evil like Sauron. He was created long before the events in Middle - earth started to unfold. Gandalf's origin story is deeply intertwined with the greater cosmology of Tolkien's world. He had powers that were both magical and related to his wisdom and knowledge, which he used to influence the course of events in Middle - earth.

Gandalf has his origin as a Maiar, a divine being in Tolkien's mythology. He was dispatched to Middle - earth to oppose the rising evil. His initial form was that of a spirit, and then he took on the guise of an old man, a wizard. His origin story is tied to the grand plan of the Valar to protect Middle - earth. He had powers that were not fully understood by the mortal races. His knowledge of the past and his connection to the higher powers were a result of his origin. And his actions, like mentoring Aragorn and guiding the Fellowship, were all influenced by his origin as a Maiar sent to Middle - earth for a great purpose.

I'm not sure which specific story Gandalf is telling as there are many in the Tolkien's works. Maybe it's about the history of Middle - earth, like the battles against the dark forces or the tales of the rings.

The Lord of the Rings series by J.R.R. Tolkien features Gandalf and his adventures extensively.

Maybe he wants to pass on knowledge or history. Gandalf is full of wisdom and stories are a great way to share it.

You could try 'The Silmarillion'. It provides background and additional context related to Gandalf and the broader Tolkien universe.