Humanity is on the brink of extinction in the future. An object called The Traveler that possess great knowledge and technology came shortly after the present day and humanity was in their golden age expanding throughout the solar system. The golden age lasted for hundreds of years. Until The Traveler's greatest enemy called The Darkness came to the solar system and wiped out most of humanity. The Traveller has been silent ever since. They built a city under the The Traveler as a last ditch resort to save the human race. The ones who guard the city are called Guardians who possess powers gifted from The Traveler. Many Alien races have come as "minions" of the darkness .and they will stop at nothing. If you fail, humanity will be destroyed.
Did You Know?
As of January 7th 2015 (nearly 4 months after its release) there are some players who have put over 2000 hour into the game. Averaging to about 16 hours and 40 minutes per day. It should be known though that leaving your console in the main screen still counts the hours, so it is likely these numbers are inflated. See more
[from 'The Taken King - Regicide'
What you call the Darkness is the end of your evolution!