We've seen queer characters in video games before, but The Last of Us 2's Ellie is probably the first openly LGBT+ protagonist in a triple-A game. In the new trailer that opened the Sony E3 conference, Ellie is seen in a romantic relationship with a character named Dina, and the two share a kiss.
Ellie being LGBT+ was revealed in the first The Last of Us DLC Left Behind, where she serves as the player character and forms an intimate romantic relationship with the character Riley. But with Ellie being the protagonist of the entirety of The Last of Us 2 and the trailer showing a big gay kiss, we're finally seeing some queer representation with a protagonist in the mainline story of a triple-A game, something that hasn't occurred outside of the indie sphere or in supplementary media, not in the actual game.
There have been a few protagonists in the past that have been LGBT+. Perhaps the most recent is Trevor Philips from Grand Theft Auto V, who mentions being bisexual in a sequence of the game. But in that instance as well as many others, it's either only off-handedly mentioned, implied, revealed by developers in interviews or comics, or is an aspect of a customisable player character like in Mass Effect and Dragon Age, which places the enacting of that representation in the hands of the player, and not as an inherent quality of the protagonist.
Even better for The Last of Us 2, Ellie's romantic interest Dina looks to play an important role in the game. The character is being portrayed by Shannon Woodward, known best for her role as Elsie Hughes in Westworld. With an actor so prolific in the role, it's unlikely that Naughty Dog would waste the character. It reinforces the likelihood that we'll see a bona fide queer relationship portrayed on the polygonal screen.