The Attack Titan was one of the Nine Titans that could see through the memories of its past and future holders, and is said to have fought for freedom throughout the course of numerous generations.
Abilities: While all of the Nine Titans could receive memories of past inheritors, the Attack Titan could also receive memories of inheritors yet to come. Zeke Yeager described it as "the power to transcend time", speculating that Eren sent specific memories to Grisha to suit him. These memories led those with the Attack Titan to move forward, fighting for freedom.
History: The Attack Titan, like all the Nine Titans, was brought into the world after the death of Ymir Fritz. Though this Titan was presumably caught up in the conflict of houses between the eight Titans of the Eldian Empire subservient to the Founding Titan, it is said that the Attack Titan always fought for freedom no matter the day and age. During the Great Titan War as Marley gradually gained control over seven of the Nine Titans, the Attack Titan evidently never fell into Marley's hands and remained on the mainland while the Founding Titan remained overseas on Paradis Island where King Karl Fritz relocated the capital.
Story: After holding the Attack Titan for approximately thirteen years, Wall Maria came under attack by the Warriors of Marley; Grisha Yeager decided the time had come to negotiate with the Founding Titan or take it by force if necessary. Arriving at the Reiss Chapel, Grisha pleaded with Frieda Reiss for the sake of Eldia and the Walls, but his cries were neglected. Although insistent about taking the Founding Titan by force, Grisha is unable to until he is pressured to by the future holder of the Attack Titan: his son Eren Yeager.
Trivia: The Attack Titan shares the same Japanese name with Attack on Titan: 進撃の巨人. Before inheriting the Attack Titan, Grisha Yeager had dark colored eyes. After inheriting the Attack Titan, Grisha's eyes became light colored.
Source: Attack Titan, available under CC BY-SA 3.0.