Character Profile: Yamato

Yamato, or Tenzou, is a true Anbu and former classmate of Kakashi, hence the 'senpai' suffix he always adds to Kakashi's name. He takes Kakashi's place in team 7's team when he is temporarily in the hospital because of the Akatsuki's kidnapping of Gaara. He takes Naruto, Sakura, and Sai (another new member of the team) to the heaven and earth bridge to meet Orochimaru's spy who was supposedly feeding Sasori information on Orochimaru. Unfortunately it didn't go as planned and Tenzou got his fake head cut off by the spy's (aka Kabuto's) medical ninjutsu. He wasn't a real spy, just trying to earn Sasori's trust so he could murder him for Orochimaru.

Tenzou has the ability to use wood style ninjutsu, or the 1st's ninjutsu, because of an experiment conducted by Orochimaru. Orochimaru was injecting kids with the 1st's DNA, and everyone died except for Tenzou who miraculously survives and is able to use wood style. Orochimaru says on the heaven and earth bridge that his experiment was apparently a success.

So far, no one knows how in the world Tenzou and Kakashi knew each other except that they were classmates. Otherwise, they were both in the Anbu at the same time so they could've been on a squad together.

Tenzou has the ability to seal the nine-tail's powers, or rather suppress them. The alias Yamato comes from Tsunade's mission to take Kakashi's place, he can't be called by his real name. It's secrecy, and Tsunade is the one who comes up with that name.