Zack Fair is a non-player character from Final Fantasy VII and the main protagonist of its prequel, Crisis Core Final Fantasy VII. The wielder of the Buster Sword before Cloud, Zack received the Buster Sword from his predecessor Angeal. Zack is a 1st clas$ SOLDIER and is Cloud's best friend during their time working for Shinra. However, after Sephiroth goes insane, they become test subjects to Professor Hojo, and Zack ultimately sacrifices himself to save Cloud's life. He is also Aerith Gainsborough's former boyfriend.

Zack acts as the protagonist of Crisis Core: Final Fantasy VII. He works as a subordinate under his close friend and mentor Angeal Hewley.Through various events, Zack falls in love with Aerith and befriends Cloud, Tseng, Cissnei, and Sephiroth. Zack is assigned to accompany Sephiroth and two grunts, one being Cloud, on a mission to Nibelheim to find the cause of a Mako reactor malfunction. While there, Sephiroth discovers his supposed origins and goes insane. Both Zack and Cloud engage him in battle, and Sephiroth is eventually thrown into the Mako reactor by Cloud. However, Zack and Cloud are too injured to continue on, and taken by Hojo for experimentation. After being experimented on for four years, Zack escapes with Cloud and begins a journey to Midgar. On their way, Zack is intercepted by Shinra armed forces. Zack is shot continually in the chest by a soldier. While dying, Zack gives the Buster Sword to Cloud, telling him to live out his own life as well as Zack's, that Cloud is his living legacy. As Cloud stumbles off towards Midgar, Zack is pulled into the lifestream by Angeal, and wonders if he had become a hero.

In Final Fantasy VII, Zack only appears in flashback sequences, which portray him as almost identical to Cloud Strife in physical appearance except having black hair. When strung together, the sequences explain a great deal about Cloud's past and his connection to Sephiroth, the game's arch-villain.