The Mass Effect franchise is known for many things, not the least of which being its dense, thought-provoking world-building. There are a number of different alien civilizations and races in the Mass Effect universe, but some of them have gone extinct before the events of the first game, being relegated to distant memory. Although these races may not exist in the worlds that players explore, their legacy lives on, and they can wind up playing rather important roles in the broader story of the series.