The Justice League has come to Titans, confirming even move major superheroes for the world of the DC Universe streaming show. While the show started slow, focusing on the individual Titans as they slowly came together, it also gradually built out the larger, fully formed DC universe that the Titans live in.
The world started with the expected things, name-dropping Batman and the Joker, Robin sneaking around Wayne Manor with Bruce and Alfred always just out of sight. Dick has a host of names in his phone's contact list, confirming even more heroes, then in came Hawk and Dove, along with a Superman Easter egg, suggesting the Man of Steel may also exist.
The most recent episode, 'Donna Troy', opens with a young Dick Grayson hanging out with young Donna Troy in Wayne Manor while Wonder Woman and Batman talk downstairs for a "Justice League thing." While we don't see any of the League, or hear of anyone other than the Dark Knight or the Amazon, the confirmation that the League exists is a big deal. Without a full membership roster, we can know of at least 3 characters that would be members, but we'll definitely be on the lookout now to see what other Leaguers could exist in the world of Titans.
We've known Batan is in Titans since the very first episode. The show has very much stuck to DC canon in the parts of Batman we have seen from his Robins, both Dick Grayson and Jason Todd, to the Batcave and Batmobile, but this version of Batman also embraces a number of Batan's crueler aspects, which is a big factor in why Dick left him and eventually quit being Robin. Even so, Batman is the world's greatest vigilante, and we've already had some other impressive examples to compare him to.
We haven't seen Wonder Woman, but through dialogue from Donna Troy, AKA Wonder Girl, we actually got a significant portion of Diana Prince's traditional canon confirmed. Naturally, she's a Amazon who comes from the island of Themyscira, where she was raised and educated by her Amazonian sisters before joining the world of man. Donna contrasts Wonder Woman against Batman by saying he punishes the guilty, while Diana protects the innocent. All in all, what we know about Wonder Woman seems to do the character proud.
Superman was a little more elusive than Wonder Woman and Batman. His symbol appeared on a t-shirt worn by Dawn Granger and on magazines, but it wasn't until the Titans finale that Jason Todd name dropped him outright. Given, the reference occurred in Dick Grayson's dream, but the dream was all anchored in real events, so a Superman reference would mean nothing if he didn't also exist in the real world.
Besides, the Titans finale included a Conner Kent and Krypto post-credits scene. Since Conner is a clone of Superman in other iterations (and has his symbol tattooed on him in Titans), there shouldn't be much question that the Big Blue Boyscout is out there protecting Metropolis and the rest of the world.
While Titans only confirmed the 3 members of DC's Trinity, Doom Patrol picked it up from there. Cyborg is introduced in the show's second episode, and while he's not a member of the Justice League (yet), he does talk a lot about it.
When Crazy Jane becomes Baby Doll, it turns out the personality is a major Cyborg fangirl. She fans over him and says he's "way cooler than The Flash," to which Cyborg responds "he's not even that fast."
Aquaman also gets confirmed via Doom Patrol. Like every other hero except Batman, he doesn't actually appear, but gets confirmed by another name drop.
This time it comes thanks to Robotman. As he teases Cyborg over losing the keys to the Doom Patrol bus, he tells him "I bet Aquaman never loses the keys."
Who Else Could Be in Titans' Justice League?
The DC Universe shows will continuially continue teasing different Justice League characters going forward. Cyborg will presumably eventually join the Justice League, but for now, he's not a member and it just joined up with the Doom Patrol. Outside of that, the next most obvious members awaiting an introduction are Green Lantern and Martian Manhunter.
With Starfire's introduction in Titans, it wouldn't be outrageous for more cosmic characters like Green Lantern or Martian Manhunter to get a reference eventually, and the door is also open to the introduction of other League members like Hawkgirl as well.
It remains to be seen just what DC Universe will actually show on screen, as even Batman's episode of Doom Patrol never showed the actor's face or gave him dialogue. What is clear is DC Universe's streaming shows take place in a fully realized world of DC comics characters, and the more time we spend there, the more of it we'll see.