Grisha Yeager's backstory is key to the events in both the Attack On Titan manga and anime. Attack On Titan is a manga created by Hajime Isayama and takes place in a world where much of mankind has been wiped out by monsters called Titans. What was left of humanity withdrew behind a walled city but the outer wall is breached when the series begins, leading to a new battle with the giants. The main character is Eren Yeager, who joins the Survey Corps to fight back against them, but in doing so discovers shocking secrets about both the Titans and himself.

Attack On Titan exploded in popularity thanks to its stellar anime adaptation, with the first season arriving in 2013. The anime ported over the manga's dense, lore-packed story in addition to its shocking violence. The franchise's popularity just increased from there, leading to a two-part Japanese movie adaptation - which received mixed reviews - various video games and even theme parks in Japan. IT director Andy Muschietti is currently attached to an English language take on the property, though it's unknown when it will head into production.

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The Attack On Titan anime will end with its fourth season, though it may have to condense a lot of complex plot if the manga is anything to go by. Towards the end of season 3, the long-teased reveal of what lay in the basement of Eren's old house led to the discovery of books from his father Grisha. Eren learned the Titans are descended from a woman named Ymir Fritz, who made some kind of deal with unknown beings that transformed her into the Founding Titan. Anyone with Titan power has a lifespan of thirteen years, and following her death, her powers were passed down to nine of her people, known as Eldians. This led to a long period of war where Eldia sought to use the Titans to build an empire that stretched around the globe, literally crushing any nation in their path.

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The Eldian's eventually seized Marley, which was then the most powerful nation in the world. Attack On Titan revealed that forces within Marley pit the various house of Eldia against one another, and were able to seize seven Titans. Eldian King Karl Fritz later self-exiled to Paradis Island, sealing himself and his people behind a vast walled city; in exchange for being left alone by Marley, Fritz vowed to never let his people spark another war. The King also wiped people's memories of life before the walls. Unfortunately, the Eldians who didn't reach Paradis were oppressed and forced into ghettos by Marley. This is where the backstory of Grisha Yeager kicks in.

Grisha and his sister were among the Eldian's born in a Marley ghetto, and one day as children they snuck out to see a blimp. They were caught, leading to Grisha's sister being killed. When he grows up, Grisha becomes part of the Eldian Restorationists, who want to recover the Founding Titan and use it to bring Marley down. He also marries Dina Fritz and has a son named Zeke; when he turns seven, Zeke gives his parents up to the Marley government, which is a key turning point in Attack On Titan.

Grisha, Dina and the rest of the restorationists are brought to Paradis Island and turned into the mindless giants that roam the landscape in Attack On Titan. Grisha is the only survivor, as one of the officers was a mole - dubbed  "The Owl" - within Marley, who transfers to Grisha the power of the Attack Titan. Finally, it's revealed that Grisha rocked up to the city walls feigning amnesia and was allowed inside. He makes a life, marrying Carla Yeager and having a son named Eren, all while plotting to find the Founding Titan to use it against Marley, which leads to the events that unfold when the manga and anime begin.

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