Zeke Yeager was the former Captain of Marley's Warrior Unit, assigned to take the Founding Titan from the Eldians of Paradis Island. He was the inheritor of the Beast Titan, and was considered to be the strongest warrior by Reiner Braun, contrasting Levi Ackerman's title of "humanity's strongest soldier." He manipulated and deceived both sides of the war between Eldia and Marley in order to achieve his own agenda of causing the extinction of his own people, which he viewed as "salvation."
Zeke was the son of Grisha Yeager and Dina Fritz, the older half-brother of Eren Yeager, and a member of the royal family from his mother's side.
In his human form, Zeke had a tall, broad, well-toned body with gray eyes, shaggy platinum blond hair, and a matching mustache that descended into his beard. He was seen wearing no shirt, loose pants, combat boots, and circular glasses. After his return to Marley, and the four-year time skip, Zeke began to sport a much more clean-cut look, contrasting his look while on Paradis Island. He had his hair cut much shorter, so that it no longer fell into his eyes, and sported a thinner beard.
Appearance: In his human form, Zeke had a tall, broad, well-toned body with gray eyes, shaggy platinum blond hair, and a matching mustache that descended into his beard. He was seen wearing no shirt, loose pants, combat boots, and circular glasses.
Personality: Zeke was a very intelligent and curious man. He tried to communicate with Mike Zacharias in order to get information about the vertical maneuvering equipment and learn about Mike's language, though such curiosity was often characterized by a marked callous detachment.
History: Zeke Yeager was born to Grisha Yeager and Dina Fritz, who were planning to overthrow the Marley government and put the Eldians back in power. Grisha was among the rebels when the Marley government announced the Warrior program, asking for Eldian children between the ages of five to seven to serve as potential Warriors, with the promise that their families would be given the title of Honorary Marleyans and be ensured freedom within the country.
Zeke Yeager in the story: Five years after the start of the Paradis Island Operation, Zeke travels with Pieck and a small number of Marleyan soldiers to Paradis Island to infiltrate the Walls. After arriving, the group locates a small village inside of Wall Rose, and chooses to turn its residents into Titans. The soldiers releases a gas laced with Zeke's spinal fluid into the air, which is blown into the village and inhaled by the villagers.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.