Tiger-Masked Anbu Member

He is an Anbu from Konohagakure.

Background
In the anime, he, Kakashi and four other Anbu were tasked with protecting the Third Hokage while he left the village to meet with the Fire Daimyō. En route, his group was attacked by disguised Root members with the intention of killing Hiruzen. During the attack, he fought Kanoto and Kanoe for sometime. As their group gained the upper hand, the disguised root members retreated after their failed assassination, but managed to separate the group from Hiruzen.

Appearance
He has long brown hair that he keeps held in a pony-tail and wears a white tiger-like anbu mask with nine line markings on it. He wears the standard attire of an Anbu of Konoha.

Abilities
As an Anbu, he is presumably a very powerful shinobi. He carries a sword hinting at skill in kenjutsu. In the anime, it was shown he had some skill with shuriken and was able to hold his own while fighting against two Root members simultaneously.

Konoha Crush
When Sunagakure and Otogakure launched an attack on Konoha, he, Yūgao Uzuki, and their Anbu team met at the Memorial Stone. After Yūgao swore to avenge Hayate, the team departed and attacked the invading shinobi after the village's civilians were evacuated.

Pain's Assault
During Pain's attack on Konoha, he, Yūgao Uzuki and two unnamed Anbu protected Tsunade as she was using Katsuyu to tend to the villagers injuries. When Pain approached the group, he and the Anbu concentrated chakra to their feet to combat their opponent's ability. When Pain unleashed a large-scale attack, he was caught in the impact and separated from the rest of the group. It is unknown what happened to him afterwards.

Trivia

 * He was the only Anbu which was protecting Tsunade to not get replaced by a more well known Anbu in the anime.