WARNING: The following contains spoilers for the Attack on Titan manga and anime. The manga is available in English from Kodansha. Season 4 is currently streaming on Crunchyroll, FUNimation, Amazon Prime and Hulu.
Attack on Titan series was launched as a survival horror fantasy, pitting a desperate humanity against the flesh-eating Titans. However, it later became clear that this series is all about international politics, schemes and destiny. In Season 4 of the anime, the Marley Empire is about to clash with the Eldians of Paradis Island again, and more than a few notable families have contributed to this situation.
Eren Yeager, for example, is a part of something much larger than himself. At first, "Yeager" was just a stylish, German-inspired name, but in the wake of Zeke Yeager's plan and the truth about Grisha Yeager, that name means a lot. The same is true for Ackerman, Reiss and Fritz. Here's how these four families helped shape the entire world.
The Yeager Family: Eldians To The Last
Eren's father, Grisha Yeager, is hugely consequential to Attack on Titan's story, and so are his wife Dina Fritz and his sons, Eren and Zeke. This Eldian family grew up in the internment zone of the Marley Empire, and Grisha and his younger sister Faye chafed under Marleyan rule. Grisha later married Dina Fritz, a woman carrying royal blood, and their son Zeke was born with an apparent destiny for the Eldians. Zeke was asked to become a double agent to help bring down Marley, but instead, Zeke turned on his parents, and Dina became a pure Titan. Grisha only escaped that fate with the help of Eren Kruger, and years later, Grisha arrived on Paradis Island and started a new family with his second wife, Carla.
Their son Eren was an ordinary boy until, in the year 845, Grisha took Eren to the wilds and turned him into a Pure Titan. Once Eren ate his father, he inherited Grisha's Attack and Founding Titans, meaning he is now in a position to help Zeke with his plan to use a non-royal Founding Titan and a royal Titan holder to activate the Rumbling and scare the entire world -- or worse. The Yeager half-brothers began as enemies, but now they are allies with the future of Eldia in mind. Where will this path lead them?
The Fritz Family
The Fritz family is an ancient one, but by the year 854, it is more or less extinct. This is the family of the Eldian kings, who ruled the world for around 2,000 years, beginning with Ymir Fritz and King Fritz long ago (around the time the Titans came to be). More recently in Attack on Titan, Dina Fritz was consequential because she carried royal blood and passed it on to her son Zeke. Once Zeke betrayed Dina and her husband Grisha, Dina was injected with the Titan serum and became a Pure Titan.
It was Dina who found the Yeager household in Shiganshina and ate Carla, destroying her ex-husband's new wife (who knows, maybe Titans can be jealous). Dina met her end a few years later when Eren accidentally used the Founding Titan power lying dormant within him to command several Pure Titans to attack and destroy Dina, Carla's killer. The "pure" Fritz bloodline thus vanished from the world.
The Reiss Family
The Reiss family is a branch of the Fritz family, operating under a new name. Around 100 years ago, when Marley defeated Eldia, some of the royal Fritzs stayed on the continent while the remainders fled to Paradis Island and renamed themselves the Reisses to hide their true nature. Further, the Reisses established puppet kings on Paradis Island, such as the "King Fritz" who ruled during the anime's first few seasons. The Reisses passed themselves off as a noble family in the periphery, while in reality, they truly controlled the Island's world. This family also possessed the Founding Titan but due to their royal blood, the Reisses were all bound by King Karl Fritz's directive to never use the Titan for war after the Great Titan War.
Eventually, Historia Reiss, once known as Krista Lenz, turned on her scheming father Rod and put an end to the Reiss family's shady ambitions. Historia then became a beloved queen, but now, her true role is to have heirs who can inherit the Beast Titan after her -- all according to Zeke's plan. Historia's genes now matter more than her deeds or words, whether she likes it or not (so far, though, she accepts the plan).
The Ackerman Family
The Ackermans are no ordinary family. They're not nobility; instead, they were experimented upon during the Eldian Empire days, leaving them with traces of Titan power in them (though they're thought incapable of actually turning into conventional Titans). This family served for a long time as the bodyguard unit of the royal Fritz family, until the Eldians arrived on Paradis Island and became pacifists. The Ackermans were immune to King Fritz's memory-wipe effect and objected to the current situation. Thus, the Ackermans were hunted to near extinction, with the few survivors promising to never tell their children or grandchildren the truth of this world. That's why modern-day Ackermans, such as Levi and Mikasa, grew up ignorant of all this.
The Ackerman family is loosely connected to Hizaru's Azumabito family as well. The Azumabitos were sympathetic to Eldians, to the point that their descendants ended up living among them on Paradis Island. They, too, were immune to the Founding Titan's memory-wipe effect and were hunted nearly to extinction for allying with the Ackermans. By the 840s, few Azumabitos remained, though one of them survived and had a child with a man of the Ackerman family, that child being Mikasa Ackerman. Mikasa is thought to be the sole Paradis Island inhabitant with Azumabito (effectively Asian) blood. That means she not only has latent Titan powers through her Ackerman lineage but royalty in her Azumabito blood. In other words, she's very special, indeed.