Catch-up guide: Everything that's happened leading up to Avengers: Infinity War

There's a lot to keep up with in the Marvel Universe. Here's what's happened so far. Photo / AP

Avengers: Infinity War makes its predecessors seem like small potatoes. The 19th film within the Marvel Cinematic Universe, it combines nine franchises and more than 30 major characters.

Audiences now have a decade's worth of people and plot points to keep track of, beginning with 2008's Iron Man, and retaining that much information would be a superhuman ability in itself.

But don't worry - help is on the way. We've created a guide to all the important happenings leading up to the new film. So is this truly the "most ambitious crossover event in history," as the facetious meme suggests? Judge for yourselves.

WHAT'S HAPPENED SO FAR?

- "Guardians of the Galaxy": Infinity Stones are created

After the universe began, the Cosmic Entities formed six Infinity Stones: Space, Mind, Reality, Power, Soul and Time.

- "Captain America: The First Avenger": Steve Rogers becomes Captain America

During World War II, Rogers successfully undergoes a government experiment in which he is injected with a super-soldier serum. He is transformed from a sickly, frail man to the peak of human physiology. At first used only as a propaganda piece, he defies orders and singlehandedly frees almost 400 captured Allied soldiers from an Austrian facility run by the villainous organization Hydra. Rogers then forms the Howling Commandos and continues to fight against Hydra.

- "Captain America: The First Avenger": Bucky Barnes becomes the Winter Soldier

Barnes falls off a moving mountainside train during a mission gone wrong with the Howling Commandos. Presumed dead, he is actually found and kept prisoner by Hydra. Hydra experiments on and brainwashes Barnes, enhancing his body with both chemical and mechanical enhancements so he could become the perfect weapon: the Winter Soldier. He is kept frozen in suspended animation for decades and only taken out periodically for missions.

- "Captain America: The First Avenger": Steve Rogers is frozen and presumed dead

After the Red Skull is killed, Rogers is left with a plane he doesn't know how to operate or stop. He chooses to purposefully crash the plane into the Arctic instead and is presumed dead. However, the plane crashes into an ice field and Rogers is perfectly preserved inside for 70 years.

- "Captain America: The Winter Soldier": SHIELD is created, and Hydra secretly rebuilds

Shortly after World War II, three of Captain America's allies - Peggy Carter, Howard Stark and Chester Phillips - create SHIELD: the Strategic Homeland Intervention, Enforcement and Logistics Division. The secret government organization is built to protect the United States from all threats. But early on, Operation Paperclip recruits multiple former Nazi scientists; among them is Arnim Zola, who secretly rebuilds Hydra.

- "Marvel's The Avengers": Clint Barton recruits Natasha Romanoff to SHIELD

SHIELD director Nick Fury sends Agent Barton to Russia to kill Romanoff, who has become one of the world's greatest assassins. But Barton recognizes her skill and instead suggests that she be recruited for SHIELD.

- "The Incredible Hulk": Bruce Banner becomes the Hulk

The government recruits respected scientist Banner to re-create the serum that created Captain America. While experimenting, Banner is exposed to high levels of gamma radiation and discovers that, when angered, he turns into the giant green monster. (Note: Edward Norton played Banner in the most recent Hulk movie, which is technically not part of the MCU.)

- "Iron Man": Tony Stark publicly becomes Iron Man

After returning home from imprisonment in Afghanistan, Stark builds a sleeker suit of armor to fight terrorists like the Ten Rings and make up for his company's wrongdoing. In the process, he discovers former business partner Obadiah Stane has betrayed him, and Stane is eventually electrocuted to death. News spreads about Stark's alter ego - now called "Iron Man" by the press - and instead of denying the claims like SHIELD wants him to, Stark declares to the entire world he is, indeed, Iron Man.

- "Thor": Thor arrives on Earth and defeats Loki

Odin banishes Thor to Earth after he makes the Frost Giants, inhabitants of the planet Jotunheim, declare war on Asgard. After Thor, Jane Foster and Erik Selvig deal with SHIELD, Loki sends the Destroyer, an Asgardian robot, to Earth to try to kill Thor. Thor and Loki fight, and the former ends up in Asgard with the Bifrost Bridge (a portal between the Nine Realms) destroyed.

- "Captain America: The First Avenger": Steve Rogers is found and unfrozen

Seventy years after he crashed a bomber plane into the Arctic, Rogers is found perfectly preserved in ice off the shore of Greenland. The super-soldier serum allowed him to stay alive, and SHIELD unthaws him.

- "Marvel's The Avengers": Loki steals the Tesseract and kills Phil Coulson

Loki uses the Scepter to control Clint Barton, Erik Selvig and other SHIELD agents, ordering them to kill Nick Fury and steal the Tesseract. Loki briefly loses the Scepter to the Avengers, but he regains it and murders Coulson. (Coulson is later brought back to life by SHIELD.)

- "Marvel's The Avengers": The Avengers unite at the Battle of New York

Erik Selvig, whose mind is controlled by Loki, uses the Tesseract to open a portal above Stark Tower. This allows the Chitauri, Thanos's personal army, to drop into New York. The Avengers fight them off and eventually capture Loki.

- "Thor: The Dark World": Thor frees Jane Foster from the Aether

Jane discovers the Aether (Reality Stone) and Malekith eventually seizes it to try to spread darkness throughout the universe. Thor and Erik Selvig defeat Malekith and give the Aether to the Collector for safekeeping in a mid-credits scene.

- "Captain America: The Winter Soldier": SHIELD falls

It is revealed that Hydra has infiltrated SHIELD for decades. Natasha Romanoff releases all of SHIELD's files to the public.

- "Guardians of the Galaxy": Battle of Xandar, where the Guardians of the Galaxy are officially formed

The Guardians of the Galaxy fight and defeat Ronan the Accuser, who attempted to destroy Xandar with the Orb. Star-Lord hands the Orb over to the Nova Corps.

- "Avengers: Age of Ultron": Ultron creates Vision

Ultron uses vibranium and the Scepter's Mind Stone to create Vision, who later joins the Avengers in fighting him.

- "Avengers: Age of Ultron": Battle of Sokovia

The Avengers, plus new additions Vision and twins Wanda (Scarlet Witch) and Pietro (Quicksilver) Maximoff, team up to destroy Ultron. Quicksilver is killed while saving Hawkeye. The devastation of this battle kills many innocent civilians and lays the groundwork for the events of "Captain America: Civil War."

- "Avengers: Age of Ultron": A new post-Ultron Avengers team is formed

After the Battle of Sokovia, a number of the original Avengers sort of retire: Stark shifts to a less intensive role; Barton retires to be with his family; Thor leaves to focus on the Infinity Stones; Banner, as the Hulk, disappears. A new team forms and consists of Steve Rogers, Natasha Romanoff, Wanda Maximoff, Vision, Sam Wilson and James Rhodes.

- "Ant-Man": Scott Lang takes on the Ant-Man mantle

Lang breaks into scientist Hank Pym's house and steals the Ant-Man suit, among other things. He later learns that he was meant to find the suit, as Pym wants Lang to become the new Ant-Man and steal the Yellowjacket suit from Darren Cross. Lang and Cross eventually fight, during which Lang shrinks to subatomic size and disables Cross's suit. Cross implodes.

- "Spider-Man: Homecoming": Peter Parker becomes Spider-Man

Parker, who lives with his Aunt May in Queens, gets bitten by a radioactive spider and gains spider-like powers. He fights local crime under the alias Spider-Man, maintaining his regular life as a high school student.

- "Captain America: Civil War": Scarlet Witch accidentally kills civilians during a mission in Lagos

The Avengers, while on a mission to stop Crossbones - also known as Brock Rumlow - from stealing a biological weapon in Lagos, Nigeria, accidentally cause civilian deaths. As a result, the United Nations ratifies the Sokovia Accords, which put the Avengers under government oversight.

- "Captain America: Civil War": T'Chaka dies and the Black Panther is introduced

A terrorist bomb in Vienna, where the Accords are set to be signed, kills T'Chaka. Camera footage suggests that Bucky Barnes is behind the attack - we later discover that he was framed - and T'Challa vows to get revenge.

- "Captain America: Civil War": Clash of the Avengers and Spider-Man's introduction

The Avengers, split into teams led by Captain America and Iron Man, fight over whether to sign the Sokovia Accords. Vision accidentally fires a beam at War Machine's Arc Reactor, causing the suit to crash and paralyze Rhodey. Those against the Accords end up on the Raft, a prison for people with superhuman abilities, but are later broken out by Captain America.

- "Black Panther": T'Challa becomes King of Wakanda

After T'Chaka's assassination, T]Challa assumes the throne. He is soon challenged by Erik "Killmonger" Stevens, who reveals himself to be the secret cousin of T'Challa and his sister, Shuri. Killmonger seeks revenge for his murdered father and is eventually defeated, but T'Challa is inspired to rethink Wakanda's isolationist policies.

- "Black Panther": Wakanda ends its isolation

In a speech at the United Nations, T'Challa says he'll open Wakanda's borders and share his country's secret wealth and technology. He also establishes a Wakandan outreach center in Oakland, California.

- "Doctor Strange": Doctor Strange trains in the mystical arts and finds the Time Stone

Doctor Strange trains at the mystical Kamar-Taj under the Ancient One and Karl Mordo. While there, he finds the Eye of Agamotto, which contains the Time Stone.

- "Doctor Strange": Doctor Strange defeats Dormammu and Kaecilius

Strange uses the Eye and its time-reversing power to trap the evil Dormammu in a time loop. He ends the loop after Dormammu agrees to banish himself, Kaelicius and his Zealots from Earth. He then returns the Eye of Agamotto to Kamar-Taj. A furious Karl Mordo leaves the Masters of the Mystic Arts after finding out the Ancient One misused magic, and he sets out to strip rogue sorcerers of their powers.

- "Thor: Ragnarok": Odin dies, unleashing Hela

Upon Odin's death, Hela, the banished goddess of death and Odin's secret daughter, is set free from millennia-long imprisonment. A vengeful Hela destroys Thor's famous hammer, Mjølnir, and knocks Thor and Loki off the Bifrost Bridge. She then massacres the Asgardian armies and installs herself as queen of Asgard.

- "Thor: Ragnarok": Asgard is destroyed, and Thor becomes its ruler

During a climactic final battle, Hela is defeated when Loki summons Surtur, a leader of one of the Nine Realms. An Asgardian prophecy that claims Surtur will be the one to bring about the doomsday event Ragnarok is proved true, destroying Asgard (and himself) in the process. Thor takes the throne and heads to Earth with the other survivors, including Valkyrie and Loki. Their ship is suddenly attacked by a mysterious enemy.