A C'tan actually. A more apt description would be a star god. It is from the Necron codex; a book, and as such it was printed with ink, so technically that is correct. Close enough. Spoiler Yup! That's the one!
I'd say a more apt description would be "Poor sentient hundreds of thousands of years old radiation eating gas cloud that was shoved in a colossal metal body by the Necrontryhards" :3
You really should, it is fantastic. They just finished up the 5th and final season this past Saturday.