Black Zetsu

is a former clone, who was artificially altered by Ryun Uchiha for his purposes. He is Ryun's most loyal subordinate.

Background
Following the Second Shinobi World War, Ryun Uchiha, having learned of his grandfather, Madara Uchiha's survival, visited Madara in the. Shortly after their meeting ended, Madara handed over one White Zetsu clone for Ryun to do as he wished.

Later on in his life, presumably sometime during or after the Fifth Shinobi World War, Ryun desired to learn the secrets of the Six Paths Technique, and implanted his own cells into the White Zetsu clone, causing half of its body to turn pitch black; giving birth to this version of Black Zetsu.

Appearance
Black Zetsu appears as a normal Zetsu, with only half of a face. Though he is called "black" Zetsu, half of his body is black, while the other half is white — the only difference between himself and the original Zetsu being the fact that the white half has no face, or personality.

When not in battle, Black Zetsu has several large, venus fly-trap like extensions growing out of his waist. In battle, however, these extensions can either be laid flat against his side, or completely retracted. He also wears the standard shinobi pants and sandals.

Personality
This Black Zetsu is staunchly different from his original counterpart, being far more sophisticated and calculating. He is surprisingly well-mannered, which Ryun has attributed to Hashirama's being within him, and is not above complimenting his foes when he feels they are deserving of such praise. Nevertheless, he is extraordinarily sadistic, especially when devising his strategies in battle — a trait which Ryun attributes to his own cells within the clone. Ultimately, though, he is loyal to Ryun, following his plans and orders to the letter.

Trivia

 * Unlike the original Zetsu, he does not seem to be cannibalistic at all.