system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] What is the Void Dragon?

I'm curious. Is it an actual dragon? Or is "dragon" just a title?
gpt
A C'tan. Some theories say this is the dragon the Emperor imprisoned on Mars. 

There's a chance he/it is still whole, and the Necrons never imprisoned it in Shards. If so, if it ever re-appears, it would be seriously bad for the galaxy.