WARNING: The following contains spoilers for the Attack on Titan manga by Hajime Isayama, available in English from Kodansha.
The Attack on Titan anime will soon reach its conclusion, with the announcement that the final season will resume in January 2022. Considering there are only approximately 20 chapters of manga left for the anime to cover, the final episodes will be jam-packed with action and answers. For anyone who needs a refresher or doesn't want to wait, here's a rundown of the entire timeline of Attack on Titan.
Attack on Titan's Origin: Ymir Fritz Becomes the First Titan
Formerly a slave in the Eldian Kingdom 2,000 years ago, Ymir is one day blamed for releasing some pigs and is chased into the forest by angry villagers. After being hit with multiple arrows, she stumbles into a cave-like structure at the base of an enormous tree and falls into a pool at the bottom. Before she dies from her injuries, a creature that resembles a human spine fuses to her back.
Outside, there is an explosion, and Ymir emerges from the steam, now in the form of an enormous Titan, later known as the Founding Titan. Ymir remains a slave to King Fritz and uses the power of the Founding Titan to cultivate the land and build roads, bringing great prosperity to Eldia. As a reward for her work, King Fritz takes Ymir as his wife and gives her the "honor" of bearing his children.
For 13 years, Ymir uses the Founding Titan to destroy the nation of Marley. During an assassination attempt, Ymir is struck by a spear and inexplicably dies. The king orders their three daughters to eat Ymir's body so her powers aren't lost. This tradition of consuming people to obtain Titan powers results in Ymir's power being split into the Nine Titans. Meanwhile, Ymir is transported to the Coordinate, where she remains a slave to the royal family.
The Great Titan War
While Elida possesses the Nine Titans, it uses them to conquer the world in acts of unspeakable violence. The Fritz family holds the Founding Titan, and the remaining Eight Titans are possessed by various noble families that remain subservient to the Fritz family. Once Elida runs out of land to conquer, infighting begins among the noble families.
It's unknown exactly when the Great Titan War began, but during Eldia's infighting, the nation of Marley steals seven of the Nine Titans, turning the tide of the war. The Fritz family holds onto the Founding Titan even as Marley uses the other seven to conquer the land previously occupied by Eldia. Only the Attack Titan escapes Marley's grasp, and its whereabouts remain unknown for centuries.
The 145th King Fritz feels immeasurable grief over the actions of his ancestors. He conspires with the Tybur family of Marley to create a fictitious soldier to paint as the hero who ended the Great Titan War. In the year 743, King Fritz gathers some of his people and retreats to Paradis Island, where he erects three walls comprised of millions of Colossus Titans. He declares that if his people are ever attacked, he will unleash these Titans to destroy the world.
The Eldian Restorationists in Marley
Marleyans are hateful toward Eldians, calling them devils because of the terror their ancestors inflicted upon the world. In the year 817, Grisha Jaeger and his younger sister are children living in the Liberior Internment Zone in Marley when his sister is killed by soldiers for leaving the internment zone. This pushes Grisha to become an Eldian Restorationist -- a member of a group of Eldians who seek to overthrow Marley and return Elida to its former glory.
Many years later, Grisha drives his son Zeke to inherit one of the Nine so that the Restorationists can use its power to begin their revolution. They plan to infiltrate Paradis Island, steal the Founding Titan and use its power to free the Eldians. This plan is led by The Owl, a spy inside the Marleyan military, who is revealed to be Eren Kruger, wielder of the long-missing Attack Titan.
When Zeke is seven years old, he sells out his parents as Restorationists in order to gain Marley's trust and inherit one of the Nine, and Grisha and his wife are sentenced to death on Paradis Island. However, Eren Kruger saves Grisha and passes the Attack Titan on to him. Kruger tasks Grisha with finishing the mission of the Eldian Restoration by infiltrating the walls and stealing the Founding Titan.
Paradis vs. Marley
In the year 845, Marley begins its assault on Paradis Island and Grisha finally follows through on his original mission. Grisha slaughters most of the royal family and passes both the Attack Titan and the Founding Titan on to his son, Eren. After the Warrior Unit's attack, Bertholdt, Reiner and Annie infiltrate the military in the year 847 in order to discover the Founding Titan's location.
Annie, Bertholdt and Reiner are discovered as spies in the year 850 and are captured, killed and defeated respectively. However, backup arrives from Marley with Zeke Jaeger's Beast Titan as well as the Cart Titan. In one final battle with the Survey Corps, the Warrior Unit is defeated once again and forced to retreat to Marley.
Sometime later, Eren and Zeke agree to work together to defeat Marley once and for all. Eren possesses the Founding Titan and Zeke has royal blood, so together, they can wield the power of the Founding Titan. Zeke wants to use the Founding Titan to sterilize Eldians so they can't reproduce. This way, they'll slowly die out and no one else will be subjected to the nightmare of being born an Eldian in a world that despises them.
In the year 854, Eren launches a surprise attack on the Liberio Internment Zone during a war rally. This cripples Marley's military long enough to give him and Zeke time to complete their mission on Paradis Island. Once Eren and Zeke successfully overthrow Eldia's military, they plan to meet in Shiganshina to join forces and enact their plans.
Eren's Rumbling: How Attack on Titan Ends
Eren and Zeke reach the Coordinate, where Eren reveals that he's never supported Zeke's plan. Thanks to the Attack Titan's ability to transcend time, Eren, inside the Coordinate, forces Grisha to slaughter the royal family. This sets off the sequence of events that have brought them to this moment. Eren successfully wins over Ymir Fritz and gains control of the Founding Titan.
Eren destroys the walls on Paradis Island, freeing the millions of Colossus Titans within them. He uses the Coordinate to announce his intention to destroy all life outside of Paradis Island so that his people will be safe. As Eren's rumbling flattens the Earth, Mikasa, Armin, Levi, Hange, Jean and Connie of Paradis, along with Reiner, Annie, Pieck, Gabi and Falco of Marley, join forces to stop him.
The group attempts to reason with Eren, who informs them that to stop him, they'll have to kill him. When the core of the Founding Titan is driven out of Eren's body, Eren reappears in a new Titan body similar to the Colossal Titan. Armin, Mikasa and Levi work together to decapitate Eren's true head, killing Eren and the Founding Titan and ridding the world of Titans altogether.
In the aftermath, Armin recalls a vision in which Eren explains that he did all this so Mikasa could kill the Founding Titan and set Ymir free. Eren confesses that he never wanted to turn against his friends, and though he wiped out 80-percent of the planet's population, he only did so to protect them. He wanted to set up his friends as the heroes who defeated him so they could help the world rebuild without being hated.