Name : Zetsu
1st Appearance : Chapter 234
Hidden Village: Grass
Rank : High Jounin Level, probably: None, Nukenin (Missing-nin)
Position : Right little finger
Partner : None or Not Yet Introduced
Affiliation : Akatsuki, possibly a Nukenin (Missing-nin) from Kusagakure (Hidden Grass)
Not much is known about the mysterious Zetsu, indeed, little more than that he is Akatsuki's spy. His head appears to be enveloped in a large Venus flytrap. The right side of his face, and likely his body, is black in color while his left side is white in color. His pupil-less eyes and superior vision suggest that he may harbor something similar to Byakugan and Ranmaru's Kekkei Genkai eye abilities. He also has the ability to not only merge with the ground but also with trees and other plants. With this, he can travel over very long distances very quickly.
His first appearance was after the and fight at the end of Part 1, which he observed in secret. He was also responsible for warning Akatsuki of the positions of the approaching Team Kakashi and Team Gai during their extraction of Gaara's biju.
He seems to have a split personality, as the white half of his face speaks only in Katakana (which could indicate a robotic voice) while the black side uses Kanji and Kana, and they seem to converse with each other. He is also a cannibal (in Ch. 261, he ate Kisame's body substitute), which fits his "venus flytrap" body.
The Leader dispatched Zetsu to recover Sasori and Deidara's Akatsuki rings since they were expected to both be killed, but Deidara survived. This highlighted some significance in the rings since Zetsu takes 's ring and Tobi asks if he can join Akatsuki in Sasori's place. This leads one to believe that a potential member must have one of the rings, which would explain why was not replaced - he took his ring with him when he left Akatsuki.