The Beast Titan is an extremely unusual specimen, having a distinctly ape-like appearance. Its body structure and facial features are like that of a primate, though it walks upright like a human and stands at a previously unseen 17 meters in height. Dark fur covers the majority of its body, with the exception of its face, hands, feet, and torso. Its arms are also elongated, with long fingers and a fully-functional thumb. The proportions of its upper body are similar to that of the Colossal Titan, possessing a massive chest and small head, as well as unusually slim arms.
The Beast Titan makes its first appearance in Chapter 35, when Titans are mysteriously appearing within Wall Rose even though the Wall remains intact. The Titan displays remarkable intelligence in its encounter with Mike Zakarius. It prevents his escape by killing his horse and ordering the other Titans not to eat him so that it can question him about the Three Dimensional Maneuver Gear. It takes Mike's gear for investigation when he neglects to respond. 
It next appears walking past Castle Utgard, seemingly ignoring those taking refuge within. Instead, it uses it's incredible strength to scale Wall Rose and disappears. Oddly, the reaction of Reiner and Bertolt to seeing it is later described by Ymir as resembling excited children. 
As the soldiers manage to fend off an attack, it suddenly turns its attention towards them. It begins to break off chunks of the Wall, hurling it like missiles at members of the Survey Corps trapped in Castle Utgard. The first shot kills their horses, and the second kills Rene and Henning. It then howls, summoning more Titans to continue the assault on the Castle. Nanaba angrily notes that it seems to be intentionally toying with them. Afterwards, it climbs over the Wall and disappears into the lost territory of Wall Maria.
The Beast Titan is said by Ymir to be directly responsible for the appearance of Titans within Wall Rose, possibly in order to "test" humanity's strength. She reveals that locating it was one of Reiner and Bertolt's primary goals and is key for them to return to their village.
In the aftermath of Eren's kidnapping by his former comrades, an investigation is performed at the village of Ragako. The investigation confirms the suspicion that the villagers had been transformed into Titans, though the means employed by the Beast Titan remain unrevealed. 
- The Beast Titan's appearance resembles several cryptids, such as the Sasquatch/Bigfoot, Yeti, and Yowie.
- It appears to have had limited or no contact with humanity for at least half a century, as it expresses interest in humanity's Three Dimensional Maneuver Gear. It also wonders whether or not it speaks the same language as Mike, though it's unknown whether this was genuine or simply mocking his terrified state.
- The Beast Titan is the first truly intelligent Titan to make an appearance. Most other Titans possessing intelligence are Titan Shifters, who are humans in control of a Titan body.