Robin is dead when Batman V Superman: Dawn of Justice begins.
Which Robin, though? That's kind of a mystery.
When the film starts, audiences will meet an older Batman with years of experience as a superhero. He'll have battled The Joker already, and per star Ben Affleck, the Dark Knight will already have taken on and lost at least one sidekick.
"He’s bitterly disappointed in the past that he’s lost this guy who fought by his side," Affleck told EW. "That character’s death must have been devastating to him, and he’s suffered. We get the sense that he’s suffered a lot of devastating losses before this movie even starts."
Of course, Robin for the purposes of this film could be anybody. Movies and TV series don't always closely follow the comics, and the story we're seeing here isn't one that's been in the comics before (at least not exactly). There is, however, a particularly strong case to be made that it's one of the first two Robins to appear in the comics: Dick Grayson and Jason Todd.
The Case For Dick Grayson
Dick Grayson would make sense primarily because most people outside of the comics mainstream don't understand that Robin is a legacy unto itself, or an internship program, or however it's currently viewed.
Dick Grayson was the Robin in the 1966 Batman TV show, and that version of Robin is still the one most people associate with Batman. He's also been featured in a pair of feature films which, while perhaps not beloved by all, were at least pretty popular at the time and made a lot of money.
There's also the fact that at one point a while ago, his grave was spotted by set spies, and in case anybody thought the pictures were fake, Warner Bros. went ahead and had them all removed from the Internet, giving the whole thing a sense of realism.
We will say that the most damning piece of evidence indicating that Dick Grayson is dead came from an unofficial photo of a grave that hasn't been seen in any of the promotional materials for the film.
Also, fairly recently in the comics, Dick faked his death to take on a new role as a super-spy who deals with metahumans -- something that they might be eager to use in the movies, in case the Titans project that's rumored to heavily feature Nightwing ever comes together.
That said, if Nightwing were to be a major player on TV, and Dick Grayson were Nightwing, they might just want him to die in the movies to avoid any brand confusion. Just ask Amanda Waller and Deadshot how their Earth-CW counterparts are doing...!
The Case For Jason Todd
Jason Todd, frankly, has always seemed kind of like the obvious choice here.
In The Dark Knight Returns, the 1986 comic book series that heavily influenced Batman V Superman: Dawn of Justice, Batman returns to action after a years-long retirement brought on by the murder of his young sidekick. When he returns to action, the older Batman is more brutal and unforgiving than he had been earlier in his career -- something seen in trailers for the film as well as the Dr. Pepper-released digital comics that tie into Batman V Superman.
In the comics, Jason's costume was enshrined in the Batcave as a reminder to Batman of his failures -- something that we've seen in the trailer (as pictured above). The fact that the costume here is vandalized by (we all assume) The Joker adds another level of probability to Jason, who was murdered by The Joker.
The death of Jason Todd also opens the door to the character returning as The Red Hood. Once The Joker's criminal identity, The Red Hood has become a popular antihero for DC Comics since Jason Todd returned from the dead with that name and a new costume to support it. The Batman: Under the Red Hood animated movie was one of the best-reviewed and best-selling of all DC's animated offerings.
For that reason, it would make a lot of sense to have Jason Todd be the dead Robin; it would allow you to capitalize on the popularity of the Red Hood later by introducing him in a Justice League or Batman film.
It would also mean that you could introduce Tim Drake -- who, frankly, had probably the best and most original introduction of any of the Robins -- without feeling like Jason had got the short shrift somehow. Introducing Tim in the next Batman movie could bring some lightness to an otherwise dark film and help Batman's journey toward moderating a little bit...much like he did for Bruce in the comics.
There's no real way to know. I'm leaning toward Jason Todd, since circumstantially it would line up with so much that's happened in the comics...but remember that the movies and TV shows rarely feel compelled to sync up with the comics, so that doesn't mean a ton.
Fearing the actions of a god-like Super Hero left unchecked, Gotham City’s own formidable, forceful vigilante takes on Metropolis’s most revered, modern-day savior, while the world wrestles with what sort of hero it really needs. And with Batman and Superman at war with one another, a new threat quickly arises, putting mankind in greater danger than it’s ever known before.