SPOILER ALERT! This article contains details of the plots of some Marvel films, including recent releases.

Image copyright Disney Image caption Why so serious? Perhaps the Avengers: Endgame cast are getting theirs heads round the ins and outs of the MCU

Marvel sequel Avengers: Endgame hits UK cinemas on 25 April and is widely expected to be the biggest release of 2019.

The film will be the 22nd entry in the Marvel Cinematic Universe, which began with 2008's Iron Man.

If you want to watch Endgame, but feel daunted by the sheer size of the MCU, never fear!

Here's everything you need to know.

What is the Marvel Cinematic Universe?

The Marvel Cinematic Universe - or MCU for short - is the shared place where all 22 films featuring the comic book characters are set.

Each tells its own distinct story but also connects with other films in the MCU, to tell an overarching tale. It's a technique Marvel Comics pioneer Stan Lee also used in his comics.

The MCU is the most successful film franchise of all time, making more than $18.2bn (£13.7bn) to date.

What order should I watch the films in?

We suggest you watch the films in chronological order, rather than the order in which the films were released.

Handily, in the book Marvel Studios: The First 10 Years, Marvel released an official MCU timeline to help you do just that.

We've added the films released since that book came out and voila, here is a handy diagram to help you organise your Marvel viewing!

Just one geeky note on the diagram. Technically the main events of Ant-Man and the Wasp happen before Infinity War, but we suggest you watch it afterwards to fully appreciate the post-credits scenes, which takes place later.

Why did Marvel start with these characters?

In 2007, Marvel was recovering from bankruptcy and had sold off the film rights to some of the company's most popular characters like the X-Men and Spider-Man.

Marvel still owned the superheroes who form the core Avengers team - Iron Man, the Hulk, Thor and Captain America - so used the early MCU films to introduce these heroes.

Marvel then brought these characters together for the crossover film Avengers Assemble. You can see a list of all the current members of The Avengers here.

The crossover was planned from the very beginning.

The first MCU film released, Iron Man, included a post-credits scene in which Samuel L Jackson's super spy Nick Fury gives the first mention of the Avengers.

I don't have time to watch all the films! What can I skip?

Image copyright Disney Image caption Make like Thanos and halve the size of the MCU

Endgame is the finale of a series of 22 films.

But, don't worry, you don't need to watch every single one to be fully prepared.

Here are the 10 films you could skip and still understand the basics of Endgame.

The Incredible Hulk - you'll learn all you need to know about the key characters here in Avengers Assemble

- you'll learn all you need to know about the key characters here in Avengers Assemble Thor - ditto

- ditto Thor: The Dark World - you don't need to see this to get the gist of Avengers: Age of Ultron

- you don't need to see this to get the gist of Avengers: Age of Ultron Iron Man 2 - Scarlett Johansson fans may not want to skip this one, as it marks her entry into the MCU

- Scarlett Johansson fans may not want to skip this one, as it marks her entry into the MCU Iron Man 3 - Robert Downey Jr is always watchable, but skipping this won't leave you confused

- Robert Downey Jr is always watchable, but skipping this won't leave you confused Ant-Man - Scott Lang and his superpowers get introduced all over again in Captain America: Civil War

- Scott Lang and his superpowers get introduced all over again in Captain America: Civil War Doctor Strange - all you really need to know is this film introduces the Time Stone.

- all you really need to know is this film introduces the Time Stone. Guardians of the Galaxy, Volume 2 - there's some nice character development here, but it won't give you new information on the final battle

- there's some nice character development here, but it won't give you new information on the final battle Black Panther - we hesitate to suggest you skip this Oscar-winning film, as it's one of the MCU's best, but other than introducing Wakanda as a location, you'll get most of the relevant information about the characters introduced here in Captain America: Civil War and Avengers: Infinity War

- we hesitate to suggest you skip this Oscar-winning film, as it's one of the MCU's best, but other than introducing Wakanda as a location, you'll get most of the relevant information about the characters introduced here in Captain America: Civil War and Avengers: Infinity War Captain Marvel - again, watch this if you can but if you're pushed for time, all you really need to know is that Carol Danvers (Brie Larson) got her powers from the Space Stone (aka the Tesseract) and she's going to be important to the final battle in Endgame. Also, the man who put together the Avengers - Nick Fury - lost his eye to an alien disguised as a cat.

What's so important about Avengers: Endgame?

Media playback is unsupported on your device Media caption Watch the Avengers: Endgame trailer

Marvel's plans for its films are structured in phases, with each one ending with an Avengers crossover movie.

Avengers Assemble spelt the end of Phase One, and Age of Ultron brought Phase Two to a close.

Endgame not only ends Phase 3 but also wraps up the series of 22 films that Marvel Studios president Kevin Feige is now calling The Infinity Saga.

The new title for the first three phases of the MCU references their overarching story, which sees the gathering of the Infinity Stones (six powerful gems that grant their owner great power) and the war against the mad Titan Thanos (Josh Brolin). You can read a complete guide to the Infinity Stones here.

Endgame will see the remaining Avengers try and rescue everyone, after villain Thanos (Josh Brolin) got hold of all the Infinity Stones and wiped out half of all living things with a snap of his fingers in last year's Avengers: Infinity War.

You can see a complete list of everyone who died here.

All bets are off as to who makes it to the finish line in Endgame, as it also coincides with the end of the contracts of some of the biggest Marvel stars.

Image copyright Getty Images Image caption Could Avengers: Endgame be the end of the road for Chris Evan's Captain America?

It's been widely reported that Chris Evans (Steve Rogers/Captain America), Chris Hemsworth (Thor) and Robert Downey Jr (Tony Stark/Iron Man) have come to the end of their contracts.

There's also been speculation that their Marvel co-stars Scarlett Johansson (Natasha Romonova/Black Widow), Jeremy Renner (Clint Barton/Hawkeye) and Mark Ruffalo (Bruce Banner/Hulk) have also reached the end of their tenure at the studio.

Though a solo Black Widow film is reported to be in the works, it could be a prequel, so there is no guarantee Johansson's character survives.

One thing is for sure though - whatever happens, it will take time for Endgame's story to unfold.

It's the longest entry in the MCU so far, clocking in at three hours and two minutes. That's the same length as the first instalment in Peter Jackson's Hobbit trilogy, An Unexpected Journey (2012).

What's the future of the MCU?

Image copyright Disney Image caption Hulk (Mark Ruffalo), probably reacting to rumours that one of the core Avengers team might not make it through Endgame alive

We can expect a major shake-up of the MCU, in the wake of Endgame.

Phase Four begins with the release of Spider-Man: Far from Home on July 5 2019.

According to producer Amy Pascal, the film "will start a few minutes after Avengers 4 wraps as a story".

Tom Holland's Spidey was one of many heroes wiped out in Thanos's Snap in Infinity War, but given his starring role in this film, we can expect he'll be alive and well before the Endgame credits roll.

New films involving other supposedly dead characters have also been confirmed for Phase Four.

Marvel Studios president Kevin Feige has confirmed Benedict Cumberbatch's Doctor Strange will return for a sequel at "some point in the future".

Chadwick Boseman is also likely to recover from his disintegration in time for Black Panther 2.

We also know a third Guardians of the Galaxy film has been confirmed, after Disney re-hired director James Gunn, but we don't know which Guardians will return for it. At the end of Infinity War, Bradley Cooper's Rocket and Karen Gillan's Nebula were the only survivors from that franchise.

Feige has also hinted that Phase Four could include a solo sequel for Brie Larson's Captain Marvel.

Also in development are new films involving super-powered beings called the Eternals, and martial artist superhero Shang-Chi.

Which Marvel characters aren't in the MCU?

Image copyright 20th Century Fox Image caption Dark Phoenix, which stars Game of Thrones' Sophie Turner, is likely to be the last time the X-Men appear outside the MCU

You might be confused about why some Marvel characters appear in films that don't connect to the MCU.

The reason for this is actually simple.

Long before Marvel Studios existed, Marvel Entertainment had sold the rights to some of its characters to other filmmakers.

Spider-Man was sold to Sony. The studio made a Spider-Man trilogy starring Tobey Maguire, and soon afterwards rebooted the franchise less successfully with Andrew Garfield as the webslinger.

However, Sony and Marvel have now agreed a partnership that allows Tom Holland's Spider-Man to appear in MCU films, while Sony retains the rights to the character.

Sony also owned the rights to Ghost Rider, and made two films about him starring Nicolas Cage, until the rights reverted back to Marvel in 2013.

Image copyright Getty Images Image caption Nicolas Cage, possibly hoping some strategically placed Ghost Rider branding might inspire Marvel bosses to greenlight a new film

The Fantastic Four series and the X-Men were sold to 20th Century Fox, though Marvel Studios expect to regain the rights to both properties this year due to a merger between Disney and Fox. The merger means Marvel could introduce these characters into the MCU in future films.

Fox also made the Deadpool movies, starring Ryan Reynolds, which sit firmly outside the MCU.

It's not clear what the future holds for this franchise, as the foul-mouthed, pansexual superhero is certainly not the most family friendly character.

However, the Deadpool films were a commercial success and star Ryan Reynolds has hinted on social media that he'd like there to be a future for the character with Disney.

Fox also owned the rights to Daredevil, in 2003 producing a film starring Ben Affleck, and the 2005 spin-off film Elektra, before the rights reverted back to Marvel.

Universal's Hulk films and New Line Cinema's Blade Films were also the result of deals struck before the rights to those characters reverted back to Marvel, and don't belong within the MCU.

I've seen all the MCU films. What else can I watch?

Image copyright Getty Images Image caption Clark Gregg looks very pleased that his character got resurrected, so he can keep cashing those Marvel cheques

Don't worry. There are plenty of TV shows set in the MCU to keep you going.

Agent Carter - follow the adventures of Hayley Atwell's Agent Peggy Carter as she reprises her role from the MCU films in this series, which ran from 2015-16.

- follow the adventures of Hayley Atwell's Agent Peggy Carter as she reprises her role from the MCU films in this series, which ran from 2015-16. Marvel's Agents of S.H.I.E.L.D. - the show that proves Avengers Assemble wasn't the end for Agent Phil Coulson (Clark Gregg).

- the show that proves Avengers Assemble wasn't the end for Agent Phil Coulson (Clark Gregg). Inhumans - this show ran on the US network ABC for one series. It centred around the Inhumans - an alien race with superpowers that gets in contact with Earth.

- this show ran on the US network ABC for one series. It centred around the Inhumans - an alien race with superpowers that gets in contact with Earth. Runaways - this show, based on the comics of the same name, is on streaming service Hulu. It follows six teenagers who discover their parents are villains.

- this show, based on the comics of the same name, is on streaming service Hulu. It follows six teenagers who discover their parents are villains. Cloak and Dagger - this series about a romance between two super-powered teenagers is on the ABC-owned Freeform network. It's based on characters who first appeared in the Spectacular Spider-Man Comics.

- this series about a romance between two super-powered teenagers is on the ABC-owned Freeform network. It's based on characters who first appeared in the Spectacular Spider-Man Comics. The Netflix Marvel TV shows - Marvel's deal with Netflix has now come to an end but you can still enjoy the edgy adventures of Daredevil, Iron Fist, Luke Cage, Jessica Jones and The Punisher on the streaming service. Ensemble show The Defenders is a real highlight. Though ostensibly set in the MCU, these shows have a darker tone and don't directly connect with any of the films.

If you've now become a die-hard fan, and really want to immerse yourself in the MCU, Digital Spy has put together a complete chronological timeline of all the films and TV shows.

You could also watch the original Marvel movie - notorious 80s flop Howard the Duck.

The feathered superhero will soon be starring in one of four Marvel Television animated series for adults, so consider this essential research.

Disney has also announced plans for several new Marvel TV series, including one based on Thor's adopted brother Loki, on their new streaming service, Disney+, so there'll be plenty more Marvel content to watch in future.

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