The new protector of Earth, as chosen by the White Lantern, is finally revealed today in BRIGHTEST DAY #23. However, thanks to a press release from DC Comics and a leaked page from Bleeding Cool, we already know that the protector is Swamp Thing, making his long overdue return to the DC Universe.
Swamp Thing has a long history with the DCU, beginning as standard Sci-Fi/monster comic fare and evolving into a fantasy/sci-fi/horror comic, most notably when writer Alan Moore revamped the series by revealing that Swamp Thing had never been human, but was a plant elemental who had absorbed memories of the dead Holland. There’s been an embargo on usage of Swamp Thing in the core DCU for years, primarily leaving him in the Vertigo universe, but Dan DiDio did mention plans to incorporate the character in the near future at WonderCon.
Curiously, the White Lantern seems to believe Swamp Thing and Alec Holland are one and the same. Some storylines toyed with the notion of merging Holland’s soul with the Swamp Thing, but I personally don’t know if those are still considered canon.
Most readers were probably first introduced to the character via the live action Swamp Thing movies of the 80s, or the early 90s Swamp Thing cartoon.