Warning: The following contains SPOILERS for Stargirl, season 1, episode 4, "Wildcat."
DC Universe's Stargirl season 1, episode 4 made mention of a villain called The Shade, who betrayed the Injustice Society. This seems to be foreshadowing something big, given that the character of The Shade has a notable connection to the legacy of Starman in DC Comics.
The reference to The Shade came in Stargirl, season 1, episode 4, "Wildcat," during a meeting between two members of the Injustice Society: team leader Jordan Mahkent/Icicle and Dr. Ito/Dragon King. The brief scene saw Dragon King reaffirming his commitment to the Injustice Society of America and their mission, assuring Icicle that he would not fail like The Wizard, nor would he betray them like The Shade did. As Dragon King spoke, the camera panned over a detail in the portrait of the Injustice Society that was easily missed when the painting was first shown in earlier episodes; a pair of dark glasses peeking out of the looming shadow of Solomon Grundy, barely visible between Tigress and Sportsmaster.
The Shade first appeared in Flash Comics #33 (September 1942) and was set up as an enemy of the Jay Garrick Flash. In his first appearance, The Shade eliminated all the light in Keystone City by means of a special machine, allowing him and his gang to loot the city blind. Later stories armed The Shade with a magical cane that allowed him to animate the shadows around him. He later became an enemy to the Barry Allen Flash as well, and was one of three villains (including The Thinker and The Fiddler) who joined forces in "The Flash of Two Worlds" storyline which was the first team-up between Jay Garrick and Barry Allen in the comics.
The Shade was never given an official background or a proper name until the 1994 Starman series. It was here that writer James Robinson established Shade as an immortal mercenary and Victorian gentleman named Richard Swift, who had developed a connection to the Shadowlands; a realm of primordial darkness and nightmare. This connection allowed Shade to fashion illusions and manifest true terrors made up of pure darkness from the shadows around him, without the need for a machine or magic cane. This connection also made Shade into something of a living shadow himself, as he bled shadow essence rather than blood and could heal himself with an effort of will. The Shade could also teleport himself and others through the Shadowlands, emerging anywhere in space he wished.
In addition to defining his background and refining his powers, the 1994 Starman series also gave Shade a new personality. The new Shade was a bored immortal, who had turned to supervillainy in the 1940s as a game, having become fascinated by the first wave of superheroes who had powers to match his own. Though largely amoral and willing to hire his powers out to anyone who could pay his fee, The Shade still possessed a unique sense of honor and fair play. He refused to commit crimes in his adopted hometown of Opal City and acted in secret to save the lives of Jay Garrick and the first Starman Ted Knight, when they were threatened by supervillains who plotted to murder them and their families. The Shade also became a mentor to the 7th Starman, Jack Knight, claiming he only wanted to make sure Opal City had a worthy hero to protect it, who loved the city and knew its history as The Shade did.
It remains to be seen what role The Shade will play in Stargirl. Given that the "Wildcat" episode that first mentioned him was written by the same James Robinson who redefined both Starman and The Shade for DC Comics, it seems likely that he will emerge at some point to join in Courtney Whitmore's battle with the Injustice Society. The Shade may even taken on a mentor role to the new Justice Society of America, though it seems likely that he will, as in the comics, refute any suggestion that he is becoming a hero himself or mending his old ways.