When the Green Lantern Corps faced its darkest hour after being nearly wiped out by the Parallax-possessed Hal Jordan, an unassuming artist named Kyle Rayner became the Corps' last, best hope after receiving his own Green Lantern Power Ring. Kyle's adventures would not only keep the Corps alive but lead to him help oversee its rebirth following the resurrection and cleansing of Hal. And as Hal and John Stewart continued to lead the Corps, Kyle went on to become the omnipotent White Lantern for a time before eventually losing his cosmic upgrade and rejoining his old friends on the intergalactic peacekeeping force.
Just as the Green Lantern Corps is powered by pure willpower and the Sinestro Corps is powered by fear, the White Lantern Power Battery is fueled by life itself, in direct contrast to the Black Lantern Corps' power source, which is derived from death. Introduced during the 2009 crossover event Blackest Night, the white light was formed whenever two different Lantern Corps' combined their respective emotional energies together to battle the Black Lanterns. In order to eradicate all life in the DC Universe, the Black Lanterns' leader Nekron attempted to kill the Entity, the living embodiment of the white light, only for it to bond to Hal Jordan and several heroes to defeat Nekron and resurrect a group of formerly dead characters. Later, while facing the devastating Third Army during the New 52 era, Kyle masters all seven energies in the emotional spectrum and transforms into the White Lantern to turn the tide of battle.
White Lanterns can create energy constructs powered by life itself and use this direct connection to the lifeweb to resurrect the dead by creating new White Lantern Power Rings and heal grievous wounds. There are apparent limitations to Kyle's use of the White Lantern's light, with him unable to restore the destroyed world of Korugar and its inhabitants to Sinestro's visible chagrin. And due to the white light being a synthesis of all the other lantern corps -- with the obvious exception of the Black Lanterns -- Kyle could channel any of the signature abilities that the other corps' possessed through their respective emotional energy.
Kyle's time as a White Lantern wouldn't last, however, especially after he received another massive upgrade by absorbing the Life Equation as he passed through the Source Wall at the border of the DCU to defeat the villainous Relic. Realizing that this power boost stands the chance of overwhelming and killing him, Kyle divides a portion of the Life Equation among seven Power Rings to prevent himself and the other White Lanterns from being consumed by the raw energy. Kyle's time as a White Lantern would come to a definite end during the DC Rebirth era when he tried to restore the Blue Lantern Corps, only for mysterious energy feedback to cause his White Lantern Power Ring to downgrade back to that of a Green Lantern and Kyle along with it.
Kyle's time as a White Lantern was actually his second brush with omnipotence after briefly wielding the power of the Green Lantern Corps' living entity Ion until the "Sinestro Corps War." And while green probably suits Kyle better than any other lantern corps in the DCU, his time as a White Lantern proved vital in protecting the entire universe from some truly nasty threats before the white light's connection to him was severed for the foreseeable future.