(from mass effect) Lt-Commander John Shepard (man version) is the hero of a science-fiction trilogy during the XXIIe century.
At this time, humanity of earth has evolved and encoutered E.T like Turians, Asari, Salarians, Krogans, Volus (and others) to become a galactic power.
But the Council at "the Citadel" has no human councelor yet... Only Asari, Turian and Salarian
are represented.
They remain the center of milky way galactic government (that's why Cerberus is in "war" against this mean of way).
To travel between star systems E.T and humans discovered unknown very advanced technology : cosmodesic relays. The first discovered by humans is the Charon relay, near Pluto.
A Legend says that every 50,000 years, mysterious giant machines called "reapers" are coming from the unknown deep space to enter the milky way and destroy all life in the galaxy.
This is where the plot begins...