Who Is the Beast Titan on 'Attack on Titan'? [SPOILERS]

The anime Attack on Titan is extremely popular. It's set to end by the winter of 2021 and the manga just ended, but new fans seem to be popping up every day since Attack on Titan is so heavily suggested to those new to anime. One of the main plot points in the series is discovering who the Titans actually are. We find out early on in the series that protagonist Eren Yeager is an Attack Titan, but there are a few other kinds we learn about as we keep watching. 

One of those kinds is the Beast Titan, who seems so much smarter than the other Titans that have attacked Eren's homeland up to that point. Over the course of the anime and manga, we find out that the Titans are much more complex and diverse than we had originally thought, while the Beast remains a mystery. But who is the Beast and how does it fit into the overall story?

It turns out that the Beast Titan is Eren's half-brother, Zeke Yeager. Before their dad, Grisha, met Eren's mom, Carla, he was married to a woman named Dina Fritz. She's from the Titan's royal bloodline, but that didn't prevent her from being forced to turn into a Titan and leave her home after she had been accused of treason. After this happened, Grisha was rescued before he met a similar fate and was able to start a new family with Carla.

It turns out that Zeke's parents were accused of treason because he ratted them out to the government and effectively severed the already strained relationship he had with them. After this, he grew to hate the Titan race, otherwise known as the Subjects of Ymir, and joined the military. He rose within its ranks for decades and eventually discovered he had a half-brother, who he wanted to join him in ending the Titan race. At the end of it all, he would succeed. 

Zeke isn't the first Beast Titan. Being a Titan is something that is passed down from one generation to the next, but how that happens is a little confusing. The soul of the first Titan, named Ymir Fritz, was split into nine parts after she died and these different parts made up the nine different kinds of Titans that her descendants would be able to transform into. In addition to the Beast Titan, there were the Founding, Attack, Colossus, Female, Armored, Jaw, Cart, and War Hammer forms.

Technically, the first Beast Titan would be the person who inherited the ability after the death of Ymir, but now, no one can naturally turn into a Titan at all. At the end of the manga, Eren dies and all Titans turned back into their human forms. 

On top of that, the source of the Titan power, called "the source of all living matter" or the "shinny centipede," vanished at the same time. This basically means that the Titan race no longer exists, but they are still discriminated against.