The Supergirl season 4 premiere may have taken the first step towards introducing Darkseid and the rest of Jack Kirby's New Gods into the reality of the Arrowverse. Surprisingly, it did this not with a grand display of special effects or an alien attack but with the casual mention of a single name that is long associated with Darkseid in the comic books.
One subplot of Supergirl's season 4 premiere, "American Alien", saw scientist Lena Luthor visiting her mother, Lillian, in prison and talking with her about the family's criminal past and how it might affect their company. Specifically, Lena made reference to how, when Luthor Corp was still being controlled by Lex Luthor, he was business partners with a man named Bruno Mannheim, whom Lena said she blamed for setting Lex upon a criminal path. Lillian agreed that Mannheim was a crook, but said that his role in running things at Luthor Corp was limited towards using it as a means of laundering money.
Comic book readers watching Supergirl will likely recognize the name of Bruno Mannheim as that of a recurring villain from the Superman books. First appearing in Superman's Pal Jimmy Olsen #139 in July 1971, Bruno "Ugly" Mannheim was one of the most powerful gangsters in Metropolis and the eventual leader of Intergang - a criminal group that acquired weapons from the planet Apokolips and used them to expand their territory. Precisely why Darkseid aided Mannheim was never explained in Jack Kirby's original comics, but it is presumed Darkseid may have just been adding to the general misery of the universe as part of his never-ending quest for the Anti-Life Equation, which would allow him to enslave all sentient life.
While not the most powerful or intelligent of Superman's enemies, Bruno Mannheim has proven one of the most resilient. Every live-action television adaptation of Superman's adventures since Lois and Clark: The New Adventures of Superman has featured Mannheim as a villain in at least one episode. He also had a major role in the first season of Superman: The Animated Series, where, as in the comics, Mannheim's mob became the foundation of Intergang and helped to pave the way for Darkseid's efforts to invade Earth.
Coincidentally, Bruno Mannheim also has an association with Kate Kane a.k.a. Batwoman, who is coming to the Arrowverse is crossover event Elseworlds. At the same time Kate Kane was introduced in the mini-series 52, Bruno Mannheim was reestablished as the leader of The Cult of Crime - a religious order based around a book called The Crime Bible, which turned criminal activity into a sacrament. Much of the story of 52 centered around a prophecy involving a "twice-named daughter of Cain" whose sacrifice in the name of The Cult of Crime would lead to her killer gaining infinite power. While it is unknown if this storyline will be recreated in the upcoming Batwoman series, it does seem odd that Bruno Mannheim would just now be mentioned as plans are being made to introduce Batwoman into the Arrowverse.
It is also worth mentioning that we know some form of Intergang already exists in the world of Supergirl in the Arrowverse, as it was identified as a terrorist group which had employed John "Metallo" Corben, in Supergirl's second season premiere, "The Adventures of Supergirl." And while nothing has been said about Bruno Mannheim making an appearance on Supergirl this season, his presence somewhere on Earth-38 would explain some of the high-tech, anti-Supergirl weapons that Otis and Mercy Graves utilized in "American Alien."Could it be that Darkseid is already beginning to deliver Apokoliptian weapons to Earth? Time will tell, but it seems a likely possibility.