Following the trope by the same name, the traveler is the game’s chosen one. Alone in the world, only they can uncover the mysteries of the galaxy. They will be deterred in their mission by a malevolent force which must be overcome for them to reach the heart of the galaxy.
Sean Murray first introduced the idea of the sentinels as a malevolent force back in 2014 during an interview with The Guardian.
“There’s also something else we haven’t shown. There is a malevolent force in the universe that does provide a lot of combat and more core gameplay at times. We wanted that; we wanted players to wander around exploring planets but never to feel entirely safe.”
So if the sentinels are the traveler’s primary antagonists and they were most likely created by the Atlas to maintain order in the galaxy, does that mean that the Atlas is actually the bad guy? You have your first interaction with the Atlas shortly after beginning No Man’s Sky and the first thing it does is offer you a path. At this point you have no knowledge at all of the galaxy and presumably no importance to it, yet this cosmic entity immediately reaches out to you. It lets you pretend that you have free will, but with no other sense of purpose you will eventually grow curious about what it offers. If you stray outside of the parameters it deems acceptable it has no qualms about letting the sentinels destroy you and starting again.
So what would be the point of this? Ultimately, the Atlas attempts to convince the traveler that they are taking part in a massive simulation. Not only that, but you are eventually tasked with contributing to growing the simulation by adding another star system. The Atlas needs the traveler to expand it’s reach across not only this galaxy, but any number of new, more far reaching ones. By manipulating the traveler and carefully cultivating what they see and learn, the Atlas manipulates us into fulfilling its purpose again and again. At least, until the player gives up leaving the Atlas to continue its rule, unchallenged.
Admittedly, there wasn’t as much lore to work with here as I’d initially hoped, but the ideas presented here are at least plausible and hopefully can add to your enjoyment of the game. That is assuming you haven’t already refunded it.