The War Hammer Titan was one of the Nine Titans. It possessed the ability to create structures out of hardened Titan flesh.
Abilities: The War Hammer Titan could produce and manipulate structures that were made of hardened Titan flesh. Such structures could be weaponized. For example, it could form pikes large enough to impale and lift a 15m Titan, flood areas with protrusions such as spikes, and manifest the Titan's signature war hammer.
History: The War Hammer Titan, like all the Nine Titans, was brought into the world after the death of Ymir Fritz. In the 1,800 years following her death, the War Hammer Titan was held in the possession of one of several of the warring Eldian houses subservient to the Founding Titan. After these seventeen centuries, when King Karl Fritz abandoned the conflicts of Eldia and relocated to Paradis Island, the War Hammer Titan had come into the possession of the Tybur family.
Story: After the Marley Mid-East War, Zeke Jaeger develops some concerns towards the fate of the Eldian race, given the world's rising technological advantage over the Titans and, by extension, over Marley. In order to improve the reputation of the Eldians in the eyes of other nations, Zeke convinces the Tybur family to support the next attack on Paradis Island with the power of their War Hammer Titan. Shortly afterward, when the Tybur family arrives in Liberio, Willy Tybur converses with Commander Theo Magath concerning the state of their nation.
Source: War Hammer Titan (Anime), available under CC BY-SA 3.0.