It's not a question of if characters will die in Infinity War, but which. Heimdall seems like a pretty likely choice. He's on the ship full of Asgardians that ran into Thanos' ship at the end of Thor: Ragnarok, and thus will likely face off against Thanos. He's not a main character, but he's popular enough that his death will mean something.

Guess who else is on that Asgardian ship? That's right, Loki. Furthermore, Loki currently has an Infinity Stone that he swiped from Asgard in Ragnarok, and we know from the Infinity War trailers that Thanos ends up with it. Thanos killing Loki after taking his Infinity Stone would certainly establish him as a serious villain.

Vision also has an Infinity Stone — in his forehead — and it keeps him alive. And although there are hints that Shuri is able to extract Vision's Mind Stone without killing him, he still may not survive the battle against Thanos.

Thanos' daughter, Nebula set out to find Thanos at the end of Guardians of the Galaxy: Vol. 2. If she finds him and tries to kill him, it's not going to go well for her.

Thanos' other daughter will likely figure prominently in the movie, since she knows the villain better than anyone. This could lead to a face-off between the characters, and Thanos killing his "favorite daughter" could further establish him as a villain unlike any other in the MCU.

As the originator of the MCU, the time has probably come for Tony Stark to pass the torch on to the next generation. His death would arguably be the most impactful of any character, and after ten years his time may be up.

Cap is widely assumed to bite the dust in the film, given that Chris Evans seems unlikely to continue in the role. Cap's character arc also sees him looking for redemption after the events of Civil War, which means a self-sacrifice may be in the cards.

All of the above characters could die... along with everyone else. In "The Infinity Gauntlet" comic, basically all of the major heroes are killed by Thanos once he has all the Infinity Stones, only to be resurrected later by Adam Warlock once he gains control of the stones. Might something similar (minus Warlock) happen in the movie?

Going off of the "everyone dies" theory, there's a related theory suggesting that the film takes place in multiple timelines or realities, which explains why so many characters (Thor, Vision, Iron Man, Captain America, Doctor Strange, etc.) seem to be killed in the trailers. These may all just be possible outcomes, with timelines being reset throughout the film — thanks to the Time Stone — in an attempt to correct them.

A related theory suggests that, at the end of the film, Doctor Strange goes back in time after all of the Avengers were killed in an attempt to give them a do-over. This is largely based on set photos from Avengers 4, which show the actors apparently reenacting scenes from the New York invasion of The Avengers.

One of the most famous scenes from "The Infinity Gauntlet" comics is when Thanos snaps his fingers and eliminates half the life in the universe. People just disappear. It's alluded to twice in the movie's trailers — by both Gamora and by Thanos himself — and seems very likely to happen on screen.

The Skrulls are shapeshifting aliens in Marvel comics, and they're confirmed to appear as villains in next year's Captain Marvel, which takes place in the 1990s. There's also a famous comic book storyline called "Secret Invasion," where it's revealed that several Skrulls have been posing as Avengers for years as part of a, um, secret invasion. Might some of those '90s Skrulls have pulled the same stunt, only to be revealed in Infinity War?

As stated, Captain Marvel takes place in the '90s, meaning Captain Marvel already exists in the MCU during Infinity War. But where is she? It seems unlikely that she's on Earth, but might Thanos' actions draw her into the fight from wherever she is?

Captain America has both retired and died at various points in the comics, and in those instances either Bucky Barnes or Sam Wilson has taken up the shield as the new Captain America. If Cap dies in the movie and his buddies survive, one of them could become the next on screen Cap, too.

The Soul Stone is the only Infinity Stone we haven't seen yet, but there's a good chance it's in Wakanda. We know Thanos invades the country in Infinity War, and he must have a reason for doing so. Also, that orange sand from Black Panther that allows people to enter a world where they can talk to their dead ancestors works very similarly to the way the Soul Stone works in the comics.

Hawkeye, whom we know is in the film, has been mysteriously — and deliberately — left out of all promotional materials for the film. What could possibly be the reason for purposely cutting one of the original Avengers out of the film's ads other than Clint Barton somehow playing a hugely important and spoilery role in the film?

These Infinity War theories seem the most likely to come true out of the various examples floating around the internet, so study up and act like you knew it was coming when Hawkeye saves the day in Infinity War and everyone travels back in time (except for Iron Man because he's a Skrull).