Akhaten

Akhaten was a parasitic, sentient planet that fed on the souls, and therefore the stories, of the Sun Singers of Akhet. He was considered by the people of the neighbouring worlds to be a great and fearful god. Within his rings was the asteroid Tiaanamat, in which was held the Festival of Offerings, which served to keep him asleep.

Biography
Akhaten slumbered for thousands of years, until the Long Song ended. Akhaten then awoke and threatened to consume all seven of its neighbouring planets. Eventually, the Eleventh Doctor let him take his memories instead of the valuable things of the natives of Akhet. The Doctor was then saved by Clara Oswald, who gave Akhaten 'the most important leaf in human history', the leaf that told all of her family's story, all that happened, all that didn't happen and all that should have happened. The overload of stories caused it to implode. (TV: The Rings of Akhaten)

Personality
As a sentient being, Akhaten had a personality - that of an evil and sadistic tyrant. It enjoyed being in control and delighted in the terror of the people who lived under its rule. It was shown to be very callous, not caring at all about the welfare of others and it destroyed the Vigil and the Mummy as soon as they had outlived their usefulness. It was arrogant and had a very high opinion of itself, believing it was a god even though the Doctor considered it as nothing more than a parasite.

Unable to communicate through words, Akhaten instead used facial expressions formed by two flaming eyes, a wide flaming mouth and even a nose. It seemed to have no sense of self-control, as it continued to eat the stories of both the Doctor and Clara, even after claiming to the Doctor that it had already consumed enough, until it had eaten so much that it imploded and died.