The Mass Effect series is built upon a legacy of science-fiction that stretches considerably into the past. Much like any science-fiction franchise, it pulls material from books and movies, but it also drags games into the mix as an inspiration. This eclectic mix of mediums gives Mass Effect a rather confusing labyrinth of vaguely recognizable elements. It might be difficult to sort out what goes where, but that's what this is for! As Mass Effect 2 is a natural progression from Mass Effect 1, we will be referring mostly to the series as a whole, rather than a specific game.

The most prominent element of the Mass Effect series is the conflict between the Protheans and the Reapers. The Protheans were a highly intelligent race that were wiped out alongside all other advanced races by the Reapers a considerable amount of time before the events of the first game. However, clues were left by the Protheans around the galaxy hinting at the existence of the Reapers and the role the mass relays play in their attack. With these hints, the Council races proceeded to uncover more and more information about the Reapers, their primary goal, and how they enter into the galaxy. There's a number of references to other settings in this simple description, from classic science fiction novels to excellent RPG games.

The most obvious reference is to the classic science fiction series Gateway by Frederick Pohl. Humans have found an asteroid laden with countless interstellar ships created by the Heechee, an ancient and powerful race that has since disappeared from the galaxy. The reason for this was later explained as a retreat into the interior of a black hole's event horizon to avoid a race of incredibly powerful energy beings known as The Foe. The Foe wipe out all advanced civilizations that come to their attention, as they regard matter as waste and energy as the true form that everything should take. The roles of the Heechee and The Foe can roughly and respectively be attributed to the Protheans and Reapers, while the role of the Gateway is similar to the mass relays.

Another obvious reference is to the long-running Berserker series of novels and short stories. This series revolves around the struggles of humanity (and other sentient species lumped into humanity) against a race of gigantic machine-life ships that seek to eliminate all life in the galaxy, from the sentient races down to the most simple of life. This is copied almost directly into Mass Effect, with the Berserkers becoming the Reapers and "humanity" separating into the Council and the Protheans. As the Reapers are not present in the main game except as the massive ship piloted by Saren in the first game, there's not much in the way of clever tactics and reasoning present in the series of Berserker stories, which is a disappointment.
A game that helped to push the themes of exploration and causality in gameplay is Star Control 2, and its influence is clearly felt here as well. In it, the humans have been enslaved by the Ur-Quan, which have gone on to enter into a civil war. On one side, the Ur-Quan want to enslave all life in the galaxy. On the other, they want to simply exterminate all life. While they are busy fighting each other, a Precursor ship piloted by a human genius goes around the galaxy recruiting races to his cause of resistance and uncovering technology left by the Precursors in order to stop the enslavement or genocide of all life. It's considered one of the best games of all time, and its excellently designed setting lends a weight to every decision that the player makes. This has yet to be replicated in quite the same way, although BioWare is certainly trying!

The last few inspirations are significant, but the parallels are not quite as strong as the ones here. Battlestar Galactica is obviously an inspiration on the visual style as well as the plot of life versus machines. Blade Runner's paranoia of machines imitating and influencing life is very much present in Mass Effect. Ringworld's sense of wonder and mystery while exploring ancient and powerful installations is preserved, while the story follows standard epic lines laid out by such franchises like Star Wars and Star Trek. Mass Effect is a patchwork of older influences used to make something new but somehow very familiar. It's original, but in the way that a rock band inspired by the Beatles is original. After all, you make what you like!