He was not human, but a member of an alien species whose true form resembled what Donna Noble called a "spiky lizard thing". Meng crash-landed his "celestial chariot" in China "a few centuries BC", and the future Emperor rescued Meng from the wreckage. Meng's knowledge was used by Qin Shi Huang to unite the Warring States and become the first Emperor. Later, Meng gave Qin Shi Huang a new, indestructible body, making him a cyborg. Both the Emperor and the robotic Terracotta Army were controlled by the chariot's warp converter.
Meng, seeking to take control of Earth, later remotely activated the Army, and switched off Qin Shi Huang in his throne room, describing him as a puppet who had outlived his usefulness. Donna used her mobile phone to interrupt the signal paralysing the Emperor, waking him up again. While Qin Shi Huang and Meng were fighting each other, Meng shot at the warp converter, which shut down the Emperor and the Army, while also burying the whole palace in an explosion. (COMIC: The Immortal Emperor)