Warning: The following contains SPOILERS for Young Justice season 4, episode 7, "The Lady, or the Tigress?"

A flashback in the Young Justice season 4 episode 7, "The Lady, or the Tigress" featured a surprising cameo by Joker, which explained why he hadn't been seen in the series since Young Justice season 1. It seems the Clown Prince of Crime fell out of favor with the organized supervillain community known as the Light, and Joker, in turn, lost what little desire he had to play nice with the other costumed criminals. Given that Young Justice largely focused upon the covert wing of the Justice League fighting the Light, it therefore made sense that Joker would not figure into the last three seasons of storylines.

Voiced by Brent Spiner (best known for playing the android Data in Star Trek), the Young Justice version of Joker only appeared in season 1 episode 14, "Revelation." The Clown Prince of Crime was one of seven members of an Injustice League who launched simultaneous terrorist attacks around the globe. It was revealed at the end of "Revelation" that the Injustice Gang was a ruse, organized by the Light to act as a scapegoat for their activities. It was a good joke on the Justice League, but Joker wasn't in on the punchline.

Related: Young Justice Turns A Batman Villain Into DC's Evil Spider-Man

The Young Justice season 4 episode "The Lady, or the Tigress" brought Joker back as part of a flashback detailing how the Young Justice version of Batgirl became Oracle. The sequence revealed Joker's reaction to being used by the Light as a sideshow attraction and not being allowed into the metaphorical bigtop of their circus. Unsurprisingly, Joker was not amused at having been kept in the dark, having found out eight years after the fact that every other member of the Injustice League was in on the gag but him. To add insult to injury, even minor members of the Light like Riddler were in on the scheme and Joker didn't appreciate the idea that the Light's leadership apparently found him less deserving of respect than a criminal who actively warned people about his crimes in advance.

Young Justice Joker at the United Nations

The end result of the schism was Joker sending a threatening message to Young Justice's Vandal Savage, warning him that he had a new act "sure to entertain the good guys and the bad." The act in question entailed taking the United Nations General Assembly (including Light member and United Nations Secretary-General Lex Luthor and former superheroes Tempest of Atlantis and Troia of Themyscira) captive, with the intention of exposing them to his infamous Joker toxin. The Light responded by contracting the League of Shadows to kill Joker, at the same time that a squad of Justice League members led by Batman worked to diffuse Joker's bombs and capture the Mogul of Mountebanks.

Beyond adding another level to the origin of Young Justice's Cassandra Cain, who was sent after Joker as part of her first mission for the League of Shadows, the flashback also explained why he hadn't been seen in Young Justice since his first appearance with the Injustice League. Given that the central storyline of Young Justice focused upon the first generation of the Justice League's junior partners and their struggles growing up while overseeing the Justice League's covert operations, there were few opportunities to naturally introduce the Joker into the narrative, even when Joker was in the good graces of the Light. Whatever else can be said about Joker, he is not subtle, and the level of danger he poses makes it unlikely the Justice League would ever send a squadron of inexperienced heroes against him after what happened to Batgirl, even under Batman's direct supervision.

More: Where Is M'gann? Why Young Justice Season 4 Is Ignoring Her