John Marshall Stewart is one of the superheroes known as Green Lantern that appear in American comic books published by DC Comics. One of the first African-American superheroes to appear in DC Comics, the character was created by Dennis O'Neil and Neal Adams, and first appeared in Green Lantern (Volume 2) #87 (December 1971/January 1972). The concept for the character came from Adams' idea of a substitute Green Lantern that better reflected the racial makeup of the world's population. John Stewart, a college graduate and architect, was conceived by Adams to portray a better representation of black people in America, with Adams also diverging from the usual lighter coloring of black characters to depict him as dark-skinned, basing Stewart's design on actor Sidney Poitier. Stewart was introduced in his debut issue and origin story as an anti-authority figure symbolizing Black Power politics. He notably refused to wear a mask, breaking superhero tradition. The early 1980s saw Stewart become the main Green Lantern. In 2007, Geoff Johns changed the character to be a former U.S. Marine in Green Lantern (Volume 4) #26 following his 2001 Justice League cartoon depiction, with which Bruce Timm removed Stewart's original "militant", "Black Panther Party"-esque characterization in favor of a military background.

Today John Stewart is one of the most popular and high-profile black characters in American comic books. Although a starring character in Green Lantern comics since the 1970s, he had a relatively low profile in mainstream popular culture until his adaptation for the 2000s animated series Justice League and Justice League Unlimited, voiced by Phil LaMarr. This led to an increase in the character's profile in comics, including a starring role in Justice League comics, and a massive expansion in the character's availability in DC Comics toys and merchandise. Wayne T. Carr was cast as John Stewart in the DC Extended Universe (DCEU) director's cut Zack Snyder's Justice League (2021) but his role was ultimately cut from the film. Aaron Pierre will portray the character in the DC Universe, beginning with the TV series Lanterns (2026).

John Stewart debuted in Green Lantern vol. 2 #87 (December 1971/January 1972) when artist Neal Adams came up with the idea of a substitute Green Lantern. The decision to make the character African American-descent resulted from a conversation between Adams and editor Julius Schwartz, in which Adams recounts saying that given the racial makeup of the world's population, "we ought to have a black Green Lantern, not because we're liberals, but because it just makes sense." Adams created John Stewart as "a college graduate who has a profession", wanting to avoid the prevailing depictions of black people at the time who he stated "don't represent the aspirations of every Black person in America", such as gangbangers. Dennis O'Neil wrote the script for Stewart's debut issue in line with Adams' intention for the character, making him a college graduate and an architect, unemployed because of the significant percentage of unemployment for black people in America in the time period. In the original script, the character's name was Lincoln Washington, which was chosen by Schwartz. Adams confronted Schwartz about the name being a slave name, after which Schwartz told Adams to choose the character's new name, and Adams chose "John Stewart". Adams intentionally colored the character a darker brown, rather than the usual lighter, khaki-like coloring done on black characters at the time. DC production manager Sol Harrison asked Adams about his divergence from the usual colors for black characters, to which he replied, "Most Black people I know are pretty dark. There are some very light-skinned people, but not John Stewart." Schwartz and Harrison initially expressed reluctance on the coloring for fear of offending black people, but went through with it after Adams stated that he does not think they would be offended by dark-skinned black characters. Stewart's original design was based on actor Sidney Poitier and he was one of the first African-American superheroes to appear in DC Comics. The character was DC's third superhero of African ancestry.

Stewart's debut issue and origin story, titled "Beware My Power!", introduced Stewart as headstrong, anti-authority, and race-conscious, a symbolism of Black Power politics, with Stewart initially conflicting with the primary, white Green Lantern, Hal Jordan. When one of the Guardians of the Universe tell Jordan that he is appointing Stewart as his substitute, Jordan sees Stewart standing up to two white policemen hassling black men and is displeased, viewing Stewart as disrespectful and having a chip on his shoulder, to which the Guardian responds, "He has all due qualifications! And we are not interested in your petty bigotries!" Feeling it was unnecessary to hide his identity, Stewart refuses to wear a mask, breaking superhero tradition. The story featured Stewart's first mission, wherein he unwillingly accepts Hal Jordan's assignment of protecting a racist politician, whose scheme of instigating a race riot Stewart later exposed.

After the issue, Stewart made scarce appearances until he became the main, full-time Green Lantern in the early 1980s.

"So anyway, now we have John Stewart. And I can tell you when I go to conventions I have adult Black males standing in front of me and they cry because of John Stewart, because they've been waiting their whole lifetime for a non-gangbanger. non-tribal-chief, college-educated Black man to be in comic books. They like that; like it a lot.”

"If you ask a kid who Green Lanterns [sic] is, the kid will say it's John Stewart.”

John Stewart has become a major recurring character in the Green Lantern mythos within the DC Universe. He became the primary character of Green Lantern vol. 2 from issues #182 through #200, when Hal Jordan relinquished his place in the Green Lantern Corps (1984–1986). He continued to star in the book when the title changed to The Green Lantern Corps from issue #201 to #224 (1986–1988). He would continue to make key appearances in Action Comics Weekly after The Green Lantern Corps' cancellation (1988). He starred in the comic Green Lantern: Mosaic, which DC spun out of Green Lantern vol. 3, with a four-part storyline titled "Mosaic" (issues #14–17). DC published 18 issues of the ongoing Green Lantern: Mosaic title between June 1992 and November 1993.