At the beginning of Mass Effect, humanity is still taking its first steps onto the galactic stage, only discovering the existence of the franchise's various alien species 30 years prior. As the human race stepped onto the galactic stage, it needed a place to start, and that's where Eden Prime comes into play.
While Eden Prime may look like a beautiful yet ordinary colony world, the planet is much more than that in the Mass Effect series.
Commander Shepard's Mission To Eden Prime
Eden Prime was the first planet Commander Shepard visited in the Mass Effect games. At first, the mission was to obtain a rare and valuable Prothean beacon that a local scientist team had found, but then the Normandy received a distress call, and Shepard's team arrived in full combat gear. The sky itself was red from flames and molten lava, and there were precious few survivors. Worse yet, robotic Geth -- mechanical terrors that hadn't been seen in over two centuries -- were all over the place.
Shepard teamed up with Gunnery Chief Ashley Williams, who is a survivor of the attack, and the bolstered team realized that the beacon was gone. They follow the trail of clues to the planet's spaceport, where the Turian Spectre Saren Arterius was preparing to ship it off-world aboard Sovereign, his giant flagship. Shepard saved the day and retrieved the beacon. However, they had a mysterious message beamed into their brain in the process. Later, Shepard learned the message was a Prothean distress signal from 50,000 years ago, warning of the "Reaper" invasion. This event, which takes place on Eden Prime, is the main catalyst for the events of Mass Effect.
Eden Prime Before And After The Original Mass Effect
Prior to the attack on Eden Prime, the world was a symbol of humanity's progress and strength. After the attack, Eden Prime's role as a symbol grew. Its people rebuilt and restored its beauty, proving that humanity could take on any challenge and win. But it's also a symbol for the Protheans, long after the fact.
Eden Prime was home to a Prothean city during the last Reaper invasion, and a soldier named Javik reluctantly escaped the flames and carnage in his escape pod. The pod's doors closed, and the next thing Javik knew, he was stepping onto a verdant world ruled by humanity. While all seemed lost, the last Prothean had survived the Reapers, and he was ready to help end them for good. Eden Prime was a graveyard for the Protheans, then became the wellspring of renewed hope against the galaxy's most dire threat. Humanity survived Saren, and Javik triumphed over even worse odds.
Not even Cerberus could tarnish Eden Prime's role as a symbol of hope. Liara wasn't the only one who knew about the hidden Prothean treasure there; Cerberus was muscling in and wanted to claim the artifact (Javik's pod) for itself. By then, Cerberus was a menace to the entire galaxy, and the Illusive Man was Harbinger's puppet. However, Commander Shepard wasn't about to let the Illusive Man win, and their team fought off Cerberus and claimed Javik. The people of Eden Prime then rallied and drove Cerberus off their world. In many ways, the choice to keep fighting together against deadly foes makes the colonists of Eden Prime a reflection of humanity and its tenacity on the whole.