It looks like the most unexpected adversary of Green Lantern may have played a sizable role in the hero's darkest chapter. When discussing his origin with Hal Jordan, the Orange Lantern Larfleeze revealed a secret that connected him to the Green Lantern's transition into the villain Parallax.
Hal may have gotten a reputation for being one of the Green Lantern Corps' premier ring-slingers, but all that went out the window when the hero fell from grace. After the villainous Cyborg Superman had Coast City destroyed, the loss of his hometown was too much for Jordan to bear. Green Lantern became the evil villain Parallax, turned on his friends and allies, and destroyed the Corps. It's revealed that Jordan's turn to villainy was actually a plot by Sinestro, who used the fear entity Parallax to corrupt his nemesis. Though Hal clawed his way back from the brink, his time as a villain was not forgotten.
Apparently, one of the most odd Green Lantern villains inadvertently helped nudge Hal Jordan towards his ultimate betrayal. In Green Lantern #41 by Geoff Johns and Philip Tan, Jordan meets the sole keeper of the Orange Light of Avarice. Curious to know about the Orange Lantern Larfleeze, Hal tricks the alien into revealing his secret origin. Larfleeze reveals that he was once a part of a bandit guild that pulled off the impossible—stealing from the Guardians of the Universe. Though they only sought a particular box, they recovered a map that leads the crew directly to the Orange Lantern Power Battery. However, the Guardians catch up with Larfleeze, who is overwhelmed by the Orange Lantern's light. They allow Larfleeze to keep the Orange Lantern in exchange for the box, and Larfleeze reveals it contains the fear entity known as Parallax.
The Parallax entity was originally trapped in the Green Lantern Corps’ Central Power Battery and its presence is why Lanterns were previously ineffective against the color yellow. But it appears the only reason Parallax was in the Power Battery in the first place was to keep it away from thieves like Larfleeze. It may not have been the Orange Lantern's intention, but Larfleeze laid the groundwork for the darkest tragedy in Green Lantern history.
Hal Jordan’s change into his monstrous alter ego Parallax was a horrifying period of time for the DCU. But Jordan was able to regain the trust of his allies and get his old position back in the Green Lantern Corps largely because his time as a villain was the machinations of Sinestro. However, the only reason Sinestro was able to find Parallax in the first place was because of the Guardians' decision to keep it on Oa in the Central Power Battery. Had Larfleeze never stolen the box, Sinestro could never have had Hal possessed by the fear entity. Ironically, in an attempt to keep the universe safe from Parallax, the Guardians wound up putting the entity into the most dangerous hands of all. Larfleeze might not be the most noteworthy antagonist, but he played a crucial role in making Green Lantern a villain.