Speculation on plot details for [The Avengers: Infinity War](tag:738027) is currently rife in the Marvel fandom and likely will be until we finally get to see the first part coming to fruition in 2018.
All we know for certain about the upcoming Avengers two-parter is that it will involve the coming together of the as yet unspecified team against the might of the mad titan Thanos as he collects (or has collected) the Infinity Stones to use in his quest. And Thanos on any kind of quest cannot be good. It also might herald the end of the Avengers as we know it (gasp), so it's going to be a pretty big event in the Marvel Cinematic Universe.
The most exciting part of the Infinity War event is that it may mark the first real melding of the cosmic side of the MCU (the likes of the extra-dimensional Guardians of the Galaxy and Doctor Strange) with the earthbound Avengers team, so how do certain characters fit into this framework?
Captain America (Steve Rogers) has usually been the centre-point for and leader of the Avengers team, leadership and fighting the good fight is just something intrinsic to his character. The central question regarding his appearance in Infinity Wars is will he survive [Captain America: Civil War](tag:994409) first?
In the [Marvel: Civil War](tag:2346746) comic book, following the surrender of the anti-registration side in order to stop the bloodshed, Captain America surrenders himself to the authorities. Whilst in S.H.I.E.L.D. custody he is subsequently shot and killed by Crossbones (Brock Rumlow) and a brainwashed Agent 13 (Sharon Charter) - both of whom are appearing in Captain America: Civil War. Uh-oh.
Following Cap's death his mantle is then taken up by none other than Bucky Barnes (The Winter Soldier) and due to the fact that Sebastian Stan announced last year that his contract is for nine films, it looks likely that the studio may go ahead and replace the original MCU Captain America with Bucky Barnes.
On the flip side Chris Evans originally signed up for six movies, which means that he would have one left on his contract after Civil War, and he's said a few times that he'd certainly consider staying on in the MCU if they wanted to keep him so, there's that.
But all that means is that if they want him to follow through on the terms of his contract they might wait until Infinity War - Part 1 to kill him off, after all, what would have a bigger impact on the Avengers team as we know it more than the death of their leader? Alternatively they could kill him off in Civil War and bring him back later down the line, in accordance with the comic book mythos.
Lastly, it's worth noting that if he doesn't die Captain America has proven himself able to wield the Infinity Gauntlet in the comics.
In order to stop the destruction of Earth by an alternate-reality version of Earth the Illuminati assembled the Gauntlet and Captain America used it to push away the other Earth and stop the planets colliding. This resulted in the destruction of the Gauntlet and five of the gems, so it came at a cost though.
Thor Odinson is doubtless going to have a central role in Infinity War due to being one of the few cosmic characters we've been introduced to thus far. A deleted scene, entitled The Norn Cave, from [The Avengers: Age Of Ultron](tag:293035) drops hints about the Infinity Stones and clarifies how Thor knows that four have been found when we were led to believe that he was unaware of the events that occurred during Guardians of the Galaxy.
In the deleted scene Thor (Chris Hemsworth) enters the Water of Sights and is possessed by the Norns: all seeing beings who control fate and destiny. Erik Selvig (Stellan Skarsgård) asks the Norns questions about how to stop Ultron and after being pretty unhelpful on that part they go on to have a bit of a rant about the Infinity Stones:
Thor/Norns: "The stone draws you all to its brilliance and you to your end."
Selvig: "The stone? From Loki's sceptre?"
Thor/Norns: "It was never his! It is of the six. The infinite six. Cannot be joined nor kept apart."
Selvig: "This stone?"
Thor/Norns: "The Mind Stone that rules perception, that moulds the mind's monsters. It carved out your will Eric and still you don't see?"
Selvig: "If Ultron has the mind stone..."
Thor/Norns: "No. Your enemies are closer."
The scene ends with Thor breaking away from the Norn's control and scrambling out of the pool; he lies there for a moment catching his breath before panting: "They don't see what's coming."
It's the first time the six Infinity Stones are explicitly referenced and it's why we see Thor heading back to Asgard at the conclusion of Age of Ultron, to find out what's going on and how it's all linked to the Stones.
And that's not the only link to the Infinity Stones that Thor has, as has been pointed out before, the second Infinity Gauntlet is kept in Asgard's weapons vault.
What happens to that Gauntlet is heavily dependent upon the events of the upcoming [Thor: Ragnarok](tag:956858) as technically the Gauntlet is currently in the hands of the traitorous Loki (Tom Hiddleston) in the guise of Odin (Anthony Hopkins).
Whether or not Thor will be able to wield the second Infinity Gauntlet in Infinity War and how he'll he able to power it remains to be seen. But it makes sense that it will be the best weapon the Avengers have against Thanos when the final battle rolls around.
Guardians of the Galaxy / Star-Lord
Now the Guardians of the Galaxy team are fairly new in terms of comic book history. Whereas Captain America has been around in Marvel comics since 1941 and Thor since the early 1960s, the Guardians as we know them now didn't appear in the canon till 2008. (There was an earlier iteration of the team under the name Guardians of the Galaxy but they existed in an alternate timeline from the Marvel-616 and featured different team members to the 2008 version.)
Given the proximity that the Guardian have experienced to Thanos over the years it does seem likely that they'll play a major role in Infinity Wars. The comic book team also features Quasar (Phyla-Vell) and Adam Warlock (Him). A very important character, Warlock may or may not appear in the MCU (there's been much contention over that point) but he is the centrepiece for the Infinity Gauntlet crisis and functions as arch-nemesis to Thanos, so I wouldn't be overly surprised if he gets introduced in [Guardians of the Galaxy Vol. 2](tag:1081113).
Warlock aside, Star-Lord (Peter Quill) in particular is an important character due to his parentage as the son of human Meredith Quill and alien J'son/Jason of Spartax, the Emperor of Spartoi.
As seen in the climactic scene in Guardians of the Galaxy, unlike most beings Star-Lord (Chris Pratt) is able to hold the Power Stone for a limited time without being immediately vaporised - presumably due to the Spartoi blood that flows in his veins.
This means that out of the characters we've met so far Star-Lord is one of the few able to handle an Infinity Stone without dying instantly, which makes him a priceless asset when it comes to facing off against Thanos in the ultimate battle.