The Marvel Cinematic Universe presents Guardians of the Galaxy's Star-Lord as a goofy, swashbuckling hero, masking his tragic past and badass feats behind a charming front. This has always conflicted with many of Star-Lord's early comic book depictions, which paint the space pirate as much more of a grim, outwardly tortured figure. In fact, one relatively modern comic reveals a kill count so massive, it forever places the rogue in a harsh new light.
Confronted by the former herald of Galactus known as the Fallen One, Star-Lord had to make an impossible choice. As shown in Annihilation: Conquest: Star-Lord #1 (from Victor Olazaba and Nathan Fairbairn), Peter Quill sacrificed an entire mining colony, using the resulting energy to prevent the villain slaughtering the millions of lives on Avaleen-4. As described in Thanos #12 and Annihilation: The Nova Corps Files #1, the death toll was over 350,000, including his own sentient ship. Peter immediately handed himself over to the Nova Corps to face justice for the deaths, despite believing that the deaths were necessary to save far, far more.
Star-Lord Is One of Marvel's Biggest Killers
Star-Lord subsequently defended the galaxy from the Annihilation Wave and Thanos, earning redemption in the eyes of the Nova Corps, but has long lived with the guilt of his actions, which remain part of Marvel canon. Part of his decision to establish the Guardians of the Galaxy with Rocket Raccoon was as a way to atone for his actions, as well as to confront his trauma from the events of the Annihilation Wave. While Peter has served the galaxy faithfully ever since, he hasn't truly confronted his past, and the hundreds of thousands of deaths that rest on his shoulders.
Star-Lord Is Driven by Guilt
Even in the MCU, Star-Lord is certainly no stranger to personal tragedy, between losing his mother, being abducted from his planet, killing his father and losing his love twice. However, these are all things that happened to Peter Quill. The aforementioned deaths in the comics were, despite noble intentions, his choice. This separates the films' comically guarded Star-Lord from the much more tortured Star-Lord of the comics. From outlook to personal trauma, Star-Lord's roots provide an incredibly dark contrast to what the hero would later evolve into. It adds a whole new layer to Peter Quill's swaggering lifestyle that he's secretly a highly traumatized killer running from his previous identity.
Justified or not, Star-Lord's biggest mistake instantly made him one of the greatest killers in the Marvel universe - making characters like Wolverine and even the Punisher look like amateurs. For whatever life-changing tragedies his MCU counterpart has faced, this massive body count paints the Star-Lord of Earth-616 in a much darker light than fans of the Guardians of the Galaxy movies would imagine.