The Zou Zou no Mi, Model: Mammoth is known to have been eaten by Jack over 20 years ago.

As the fruit hasn't yet been shown in the anime, we don't know a lot about its appearance.

This fruit allows the user to transform into a full or a hybrid mammoth at will. When the user transforms into them they're granted a massive frame. As it is an Ancient Zoan-type fruit, it grants the user greater strength than a normal Zoan.

In the hybrid form, the user is granted a centaur-like body with four mammoth legs, a peculiar case for Zoan users. They have an upper body if a man with a head, trunk, and tusks. In this form, the user is small but still large. They're also fast and can even use weird weapons for fighting.

A weakness of this fruit is that when the user is in their full form, they tend to become extremely heavy and slow, leaving them wide open for high-speed attacks. They also have the standard devil fruit weakness: the inability to swim.

Jack uses his devil fruit powers for combat purposes. He can cause massive amounts of destruction only with a single attack. He can trample anything that comes his way. He also uses his trunk by swinging it and damaging his opponents and surroundings.

In his hybrid form, Jack can wield both his Saitek blades and use his Devil Fruit to augment his swordsmanship. As he is a fisherman, Jack cab also remains conscious and breathes underwater without any problems.

Q. What does Zou mean?

A. Zou in Japanese translates to elephant.

Q. Who ate the Zou Zou no Mi, Model: Mammoth?

A. Jack is the person who ate the Zou Zou no Mi, Model: Mammoth.