Shiro

Shiro is a dog who appears within Tsunade's dream world.

Personality
From what has been seen, Shiro appears to be a very happy and jumpy dog.

Jiraiya Shinobi Handbook: The Tale of Naruto the Hero
Shiro is seen with Itachi and Sasuke, when Naruto arrived at their house.

Trivia

 * When written as "白", "Shiro" means "white", while "城" means "castle" and "代" means "substitution".
 * It is unknown if Shiro was ever a real dog as he was only ever seen in the Infinite Tsukuyomi dream world.