In the DC Universe, John Stewart is primarily known for being a Green Lantern, but a new GL book flips that on its head. Gabriel Hardman and Corinna Bechko's Green Lantern: Earth One Vol.2 continues its predecessor's unique take on the Green Lantern mythology and expands upon it by introducing us to a version of John Stewart that is a heroic Yellow Lantern. However, while this story sees Stewart don a yellow ring for the first time, it's far from the only time he has traded in his role in the Green Lantern Corps for something else.
A frequent and respected presence among his fellow Green Lanterns, Stewart has regularly been called upon to take a different role, be it to serve as a guiding presence to a fresh new team like with the Darkstars, or as an unwilling participant in a villainous new Corps such as the Ultraviolet Corps. John's served in many different roles across the Cosmos, and these certainly won't be the last ones.
Guardian of the Universe
Gerard Jones, Joe Filice, and Luke McDonnell's Green Lantern: Mosaic #18 saw the loyal lantern John Stewart become the first mortal Guardian of the Universe. John was dubbed the Master Builder after he became the caretaker for Mosaic World and drew upon his architectural skills to forge it into a new society. In reward for reaching this new level of awareness, he was reunited with his late wife, Katma Tui.
This new role was short-lived however, as a Parallax-possessed Hal Jordan destroyed the Guardians and the Central Power Battery. Subsequently, John was stripped of his newfound powers and his resurrected wife.
Darkstars
After the destruction of the Green Lantern Corps at the hands of a possessed Hal Jordan, an offshoot of the Guardians known as the controllers created the Darkstars. Intended to fil the void left by the decimated Green Lantern Corps, the Darkstars became corrupt and inconsistent intergalactic peacekeeping force.
Seeking to bring order to the young space force, the controllers conscripted the veteran Green Lantern, John Stewart, to bring order to the Darkstars. Despite valiantly serving them, the Controllers would eventually abandon the Darkstars leaving Stewart to fight a brutal battle against Darkseid's son Grayven. Due to injuries suffered in the battle, Stewart would resign from the Darkstars.
Indigo Tribe
During the War of the Green Lanterns event, Oa is invaded by the rogue Guardian Krona, who restores Parallax into the Central Power battery. This forced John Stewart to abandon his green ring to escape the yellow impurity. Hal later gives Stewart Indigo 1's ring in Geoff Johns and Doug Mahnke's Green Lantern #65.
Initially, Stewart struggles to use the Indigo Power Ring powered by compassion. Eventually, he masters its abilities to the point he can tap into the remnants of the Black Lantern Corps. After the yellow impurity is expunged, Stewart switches back to his familiar green ring.
Star Sapphire
The Star Sapphire Corps consisted entirely of women until Robert Venditti and Francis Portela's Green Lantern #36, where John donned a Star Sapphire ring. When the Highfather decides that no mortal should wield the power of the emotional spectrum, Stewart joins his fellow Lanterns in a search for weapons to fight back against the New Gods. Stewart is forced to make use of a Star Sapphire ring to teleport himself and his crew out of danger when they are eventually tracked down by the New Gods.
However, Stewart's time as a Star Sapphire was short-lived. Stewart would lose his ring when the Lanterns found themselves trapped on New Genesis and stripped of their collective rings.
Ultraviolet
John Stewart became the Ultraviolet Corps' first recruit when Sinestro unlocked the invisible emotional spectrum during Scott Snyder and Jorge Jimenez's Justice League #2. Sinestro believed Stewart would be drawn to the darker aspects of the emotional spectrum and chose to recruit him first. The ring is powered by a sentient sun known as Umbrax, bringing out the negative emotions of its wearer.
However, Stewart is eventually able to overcome the influence of Umbrax off the strength of his pure will. This allows Stewart to confront the negative emotions he harbors deep down and wield the Ultraviolet light for his own use.