Green Guardsman (AKA: Kyle O'Brien) is an Amalgam Comics superhero whose true appearance was Iron Lantern #1, though his metafictional appearance in the Amalgam universe was Showcase of Suspense #84, in a story entitled "The Other Iron Lantern". He was an amalgam of Kevin O'Brien, the Guardsman and Kyle Rayner, the then current Green Lantern.
When Hal Stark was called away, he trusted the power-battery to his assistant, Kyle O'Brien, who became Green Guardsman during Iron Lanterns' absence from Coast City.
When Iron Lantern returned and resumed his post, Kyle was mocked by others and named "substitute". Using this as a trigger, Mandarinestro promised Kyle that he could have the power to become the Green Guardsman again and replace Iron Lantern forever, and successfully stole the power-battery during a fight against Madame Sapphire.
In the unpublished Iron Lantern #2, Kyle bought the Power Battery to Mandarinestro as promised, but was about to be killed as his usefulness had expired. Instead, he fought Mandarinestro, giving Iron Lantern and Madame Sapphire enough time to arrive, along with Tagak the Lantern Lord.
Kyle became Green Guardsman once again, and helped to defeat Mandarinestro once and for all.
Justice Guild of America
In a Golden Age tribute story on the cartoon television show Justice League, a hero named Green Guardsman was shown as a member of the Justice Guild of America (a thinly veiled version of the Justice Society of America). This Green Guardsman had no connection to the Amalgam Comics character, and was based entirely on Alan Scott. As a child Green Lantern John Stewart was a fan of this Green Guardian's comic book adventures.