The producers were requested to specifically not cast the Sinestro Corps, the classic archenemies of the Green Lanterns, but instead showcase other Corps within the show. The show featured Red Lanterns, Star Sapphires, Blue Lanterns, the Orange Lantern and homaged the Black Lanterns; the only other Lantern colors they did not feature are the Indigo Tribe and the White Lanterns.
Razer and Aya were characters who were created exclusively for this series.
Josh Keaton, the voice actor for Green Lantern/Hal Jordan, was virtually unfamiliar with Green Lantern and read Green Lantern: Rebirth to get an insight into Hal's backstory and motivations and based his performance on "Green Lantern: Secret Origin" after reading that story arc.
The show runners did have to tone down the designs for one of the Star Sapphires, but that was long before anyone knew what time the show would air. Broadcast Standard & Practices thought she was too naked.
In proactive effort to keep the show faithful to what was going on in the comics at the time, it was decided to use the Red Lanterns as the main villains.