Avengers: Endgame is the culmination of a decades worth of movies in the Marvel Cinematic Universe. It is 22 movies in the making, which means it has elements of many of the movies that served as its foundation.

As such, the Russo brothers made sure to drop some very interesting connections to past MCU movies. Some were under the radar while others were very integral to the plot of the movie.

With time travel in the mix, this means we got to visit many key MCU movies that served as fantastic throwback moments. However, we are also treated to plenty of other moments to pay homage to the MCU. Here are the best throwback moments in Avengers: Endgame.

The Avengers

In The Avengers, Loki invades Earth trying to take over the planet for Thanos with his Chitauri army. Unbeknownst to him, he is wielding two Infinity Stones, the Mind Stone (Loki's scepter) and the Space Stone (the Tesseract). This provides a great opportunity for the Avengers to capture two of the six stones. (Three stones are in New York at the time, but more on that later.)

This sets up some nice call backs to the first Avengers movie, including giving us a look at Loki who is otherwise dead. The Avengers manage to secure the Mind Stone in a funny interaction between future Captain America and 2012 Captain America, but things go wrong with the Space Stone when Hulk smashes through a door knocking out future Tony Stark. This unfortunate fumble gives Loki the opportunity to scoop up the Tesseract and escape forcing the Avengers to find a new place in time to locate the Stone.

Another nice throwback moment from The Avengers is when Black Widow and Hawkeye are traveling to Vormir on the Milano and Hawkeye remarks this is far away from Budapest. This is a call back to a conversation they have in the movie about remembering Budapest differently. It's quick but a earnest moment between the two characters who soon part ways forever.

Avengers: Endgame review: Utterly magnificent

Doctor Strange

The Avengers end up figuring out that the Ancient One (Tilda Swinton) also happens to be in New York at the Sanctum in 2012, the same year as the Battle of New York. She is carrying the Time Stone within the Eye of Agamotto, years before Doctor Strange hands over the Stone to Thanos. This a prequel of sorts to Doctor Strange, as we meet the Ancient One before she becomes Doctor Strange's mentor.

Hulk is the Avenger dispatched to convince her to hand over the Time Stone in order the save billions of people. He does so by confirming that Doctor Strange willingly handed over the Time Stone to Thanos, which is when she discovers that this is the only way to stop him.

Guardians of the Galaxy

When we first meet Peter Quill (a.k.a. Star-Lord) in the first Guardians of the Galaxy, he is on Morag searching for a mysterious orb in 2014. Little does he know that it houses the Power Stone, which Thanos is after. He sends Ronan, Gamora and Nebula to retrieve the Stone establishing their roles in the MCU storyline.

Nebula and War Machine travel to this time to locate it, which they do with great ease. They drop in on Quill as he's singing along to Redbone's "Come and Get Your Love." However, things go haywire when future Nebula's memory gets entangled with 2014 Nebula, inadvertently warning Thanos that the Avengers are trying to undo his master plan.

Avengers: Infinity War

In Endgame, Black Widow and Hawkeye travel to Vormir to locate the Sould Stone four years before Thanos shows up with Gamora in Avengers: Infinity War. This is where we get a chance to relieve one of the most heartbreaking moments in the MCU in which we got to understand Thanos much better.

The two are greeted by Red Skull and are forced to make a life sacrifice to attain the Stone—a soul for a soul. The two battle it out, but in the end, Black Widow is the one who makes the sacrifice with her life.

Thor: The Dark World

The last stone the Avengers need to locate is the Reality Stone, which makes its first appearance in the MCU in Thor: The Dark World. When a mysterious dark power shows up on Earth, Jane Foster tries to figure out what it is only to be infected by it. The dark power turns out to be the Aether, better known as the Reality Stone.

Thor and Rocket travel to the events of the movie and retrieve the Stone from Foster. This part is quite emotional for Thor as he shares a loving reunion with his mother, Frigga. Eventually the two retrieve the Reality Stone and Mjolnir.

5 things missing from Avengers: Endgame

Avengers: Age of Ultron

During a relaxing scene in Avengers: Age of Ultron, all of our favorite heroes are having a little get together when they begin a game of trying to pick up Thor's hammer, Mjolnir. To no one's surprise, no one manages to pick it up, but Captain America does move it slightly resulting in a slightly panicked Thor.

Avengers: Endgame pays off this moment when Captain America wields Mjolnir as his new weapon to battle Thanos. It's a winning scene that gave fans something they have been waiting for years to see.

Captain America: The First Avenger

At the end of Captain America: The First Avenger, Cap is forced to dive the plane filled with destructive weapons on board or risk killing millions. This leads to an excruciating goodbye with Peggy in which he promises a raincheck on a dance they had planned.

He never is able to make that up, or that was until time travel is discovered and he has a second opportunity to make up for missing out on living a life with the love of his life when he is returning the Stones to their respective timelines. The last scene in Avengers: Endgame is of Cap dancing with Peggy, finally making good on his promise.

Tony Stark

Tony Stark is the titular character in the Avengers: Endgame with its being his swan song. This was the movie we say goodbye to Iron Man. Understanding that, the Russo brother made sure to drop plenty of throwback moments for the most famous Avenger.

When Ant-Man gets out of the Quantum Realm and he is walking around trying to figure out what is going on, he meets this peculiar kid that locks eyes with him. Later one, we see this kid at Tony Stark's funeral near the end of the movie. Who is this kid?

His name is Harley Keener, and he's the kid who befriends Tony Stark in Iron Man 3.

After the Avengers lost track of the Space Stone in 2012, they travel back to 1970 when the Stone is housed in a SHIELD base in upstate New York. Coincidentally, Tony's father happens to be working in the base and the two share a personal conversation right as his father is getting ready for his birth. It's a touching moment, as Tony never really had a great relationship with his father while he was alive before his untimely death in 1991 at the hands of Winter Soldier.

Then, during his funeral, as Tony's body is laid on the lake, you can see his original arc reactor that helped his power the Mark I suit along with the "Proof Tony Stark Has a Heart" base Pepper Potts outfitted it with. It's a great call back to the first Iron Man movie that started it all in 2008. This is when we are first introduced to the genius, billionaire, playboy, philanthropist and we've loved him ever since.

Speaking on Tony Stark's funeral, Happy Logan is consoling his daughter Morgan when he asks her if she is hungry. When she says yes, he asks her what she wants to eat and she answers cheeseburgers. This is another callback to the first Iron Man movie when Tony escaped the cave and comes back home. The first thing he wants to eat is a cheeseburger, which Happy acquiesces to and takes him to Burger King.

Lastly, at the end of the credits, you can hear a clanking sound. That sound is Tony Stark banging away in the cave in the first Iron Man movie as he is constructing the first ever Iron Man suit back when things were much simpler and we had no idea what we were getting into.