Tyrannosaurus is a small, white mouse, with a long hairless tail, red eyes, and a cheerful look on its face.
Most of the time it stands on his rear legs, keeping its front legs raised in a standard mouse pose somewhat resembling a Tyrannosaurus Rex, which probably gave it the name.
Over the last two years, it has grown to several times its original size, going from being able to fit in Iceburg's pocket to about the size of its master's head.
After the two-year timeskip it is seen wearing a collar as well as a small vertically striped suit.
Tyrannosaurus spends most of its time lying in Iceburg's pocket and squeaking happily when Iceburg caresses him.
It is apparently very loyal and attached to Iceburg, as it is always seen with him. During the fire at Galley-La Company's headquarters, instead of running away, it remained by its master's side, trying to wake him up with squeaks in order to save him.
Water 7 Saga
Tyrannosaurus is always seen together with Iceburg; it appeared the first time in his pocket, when Mikazuki was bothering Paulie at Dock 1, before being defeated by him and the other carpenters along with his crew.
When Iceburg met the Straw Hat Pirates, he said that he had recently picked up this mouse and then gave it the name Tyrannosaurus. He requested Kalifa to get Tyrannosaurus some rodent food and a cage, which she had already done for him.
During Iceburg's convalescence, it was always by his side, standing on his bed.
Later, during the fire at the company's headquarters at the hands of the CP9, instead of running away, it tried to wake up Iceburg, without success. It, alongside his master and Paulie, were fortunately saved by Tony Tony Chopper, and it spent all his others appearances together with Galley-La's president.
Where Are They Now
It was later seen during Iceburg's audition for a new secretary, lying in Iceburg's pocket as usual.
From the Decks of the World
Two years later it is still with Iceburg and his 10 year old secretary.
From the Decks of the World: The 500,000,000 Man Arc
When Franky's new wanted poster reached Water 7, Tyrannosaurus was inside Iceburg's pocket while he and his acquaintances looked at the poster.
- Tyrannosaurus was picked up by Iceburg not long before the meeting with Luffy. Iceburg also gave it the name during that occasion.
- One Piece Manga and Anime — Vol. 34 Chapter 323 (p. 15) and Episode 230, Tyrannosaurus debuts.
- One Piece Manga and Anime — Vol. 34 Chapter 326 (p. 8) and Episode 231, Iceburg introduces Tyrannosaurus to Luffy, Usopp and Nami.
- One Piece Blue Deep: Characters World (p. 107), Tyrannosaurus's birthday is given.
- One Piece Manga — Vol. 66 Chapter 655, cover story: From the Decks of the World Vol. 37.
- One Piece Manga — Vol. 50 Chapter 487, cover story: Where They Are Now Vol. 2.
- One Piece Manga — Vol. 81 Chapter 816, cover story: From the Decks of the World: The 500,000,000 Man Arc Vol. 10.
- One Piece Manga and Anime — Vol. 34 Chapter 326 and Episode 231, Iceburg introduces a little mouse he recently picked up to Luffy, and names the mouse Tyrannosaurus.