"SOLDIER 2nd Class Zack, on the job!" —Zack Fair Zack was born in the town of Gongaga, and like many boys of his generation, dreamed of joining SOLDIER to become a 1st Class like the legendary Sephiroth. He left Gongaga and joined the Shinra Electric Power Company's military forces around the age of 14 in 1997. By November 2000, he has reached SOLDIER 2nd Class under the tutelage of SOLDIER 1st Class Angeal Hewley. Angeal's words of wisdom and strong sense of honor had a profound effect on Zack, who wants to be just like his mentor. During his time in SOLDIER, he becomes friends with 2nd Class SOLDIER Kunsel, who guided him in the ways of Shinra. Zack works under Director Lazard Deusericus in the 49th Floor of Shinra Headquarters, along with many other SOLDIER members.
In Crisis Core -Final Fantasy VII-, Zack first appears in a digital training session with Angeal Hewley, who seems disapproving of his reckless attitude towards his enemies and himself. Despite this, he approves of Zack as a member of SOLDIER, and requests to Director Lazard that he be promoted to SOLDIER 1st Class and be sent on his own mission in Wutai. Shinra had been at war with the Wutai for a good time by now, and SOLDIER 1st Class Sephiroth had already become a hero of Shinra for his actions there.
Though Zack was ecstatic over Angeal's suggestion, he received some interesting news during the briefing: 1st Class SOLDIER Genesis Rhapsodos had deserted Shinra, taking an untold number of 2nd and 3rd Class warriors with him. He had to be found and stopped.
After Zack took out the forces of Fort Tamblin singlehandedly, he met with warriors in strange armor. Sephiroth identifies them as copies of Genesis. Realizing that these were the soldiers that Angeal had last been seen fighting, and that he was nowhere to be seen, Sephiroth comes to the conclusion that Angeal left with his long-time friend, Genesis. Zack however, refuses to believe that his mentor would ever desert Shinra.
Zack now begins to fight against the forces of Genesis while meeting up with several other characters of Final Fantasy VII and uncovering the truth behind Project G. He first fights armies of Genesis Copies in Genesis and Angeal's hometown of Banora Village with the Turk Tseng one month after the Wutai mission. Zack's hopes are shattered, however, when he finds Angeal standing over the body of his dead mother, Gillian Hewley. Zack is horrified that Angeal could do something so horrible to his own family, and is badly shaken. He attempts to talk to Angeal, but the latter only says, "The mother could not continue to live...and neither can the son," and walks away. After Zack defeats Bahamut, whom Genesis had summoned, he questions Genesis about what happened to his dreams and honor. Unfortunately, Genesis only declares that they are monsters and flies away on a black wing hidden beneath his coat, leaving Zack as Tseng arrives to pick him up as the village is bombed.
In April 2002, Zack is at Shinra Headquarters when Lazard gives him the title of SOLDIER First Class (most likely to replace all the Firsts who are gone). Zack is not happy that he attained his dreams so early, and after so many losses. But then, Genesis's army attacks Midgar, and Zack has to fight them throughout the city. Along the way, he saves Cissnei, another member of the Turks. Sephiroth and Zack both head to the Sector 5 Reactor to find the rogue Dr. Hollander, who is suspected of working with Genesis. Zack chases Hollander through the Reactor until he runs into Angeal, now with a white angel wing and believing himself to be a monster. Refusing to fight his old friend and mentor, Zack lets Angeal drop down into the Slums.
Zack wants to repay Aerith with one date, but she tells him not to be silly, and then later accepts.Zack drops through the roof of a church, where Zack meets Aerith Gainsborough. Grateful to her for saving his life (although she insists that she did nothing but say, "Hello-o!"), Zack offers to pay Aerith back with one date. Zack suggests that Aerith should sell the flowers that only grow in the church. Later on, Zack gets his wallet stolen by a child, and would eventually find him, only to find that the child's wallet was eaten by a monster. In generosity, he lets the child keep his wallet in order to buy some medicine, or you can choose to take the wallet back from the monsters. That being done, it happens that the kid had a lot more money in his wallet than in Zack does in his. Zack then buys Aerith the ribbon that she is seen wearing throughout the series. It was also revealed in a DMW reel that Zack wants Aerith to wear all pink when he was around. However, their date is cut short when Zack has to return to the Midgar Plate to defeat Genesis. He protects Professor Hojo during this time. Angeal rejoins Zack, and together they drive Genesis out of Midgar. Zack has to face Bahamut Fury while Angeal deals with Genesis.
In the autumn, Zack is sent to the mountain town of Modeoheim, with Tseng accompanying him once more, as well as several Shinra infantrymen, one of whom is Cloud Strife. Their helicopter is shot down by Genesis' troops on the way there, and the team must hike their way across the snow. Zack and Cloud make headway fast. When Zack makes the comment that his companion can at least keep up after seeing how far behind Tseng and the other troops are, they learn that they are both "country boys" and become immediate friends. From this point on, Cloud begins to accompany Zack on many missions and start to look up to him as a hero and role model, not unlike Zack looking up to Angeal.
They eventually come up on a Mako Excavation Facility that Zack must infiltrate while Tseng and the troops continue on to Modeoheim. Inside, Zack finds Genesis and Dr. Hollander arguing. He confronts Genesis while Hollander squirms away. Eventually defeating the degrading Genesis, Zack watches while the former SOLDIER lets himself fall into the depths of the reactor. Assuming him dead, Zack hurries after Hollander.
Inside a ruined bath house, Zack finds Hollander and Angeal. He learns here that Angeal's biological father is actually Hollander, who used the late Gillian Hewley as a test subject for Project G. It is also revealed that Angeal did not kill his mother, but that she killed herself. Although Hollander refers to him as the perfect soldier, Angeal refuses this title and, accepting the monstrosities of Project G, renames himself as the "perfect monster". He then fuses with several Angeal copy monsters and becomes Angeal Penance.
Zack inherits the Buster Sword from Angeal.Zack is forced to fight and kill this creature, obtaining the scar shown in Advent Children. Angeal is left barely alive, and apparently degrading from the wounds. Using his last strength, he hands the Buster Sword to Zack, telling him one final time to remember his dreams and honor to be a true member of SOLDIER. Distraught over the death of his mentor and friend, Zack finds comfort in the arms of Aerith, strengthening their relationship to its strongest. As one of the last 1st Class SOLDIERs, and with the war with Genesis considered over, Zack takes over Angeal's job of being the emotional heart of the organization. He meets another SOLDIER member named Luxiere, who also looks up to him as a role model, and constantly sends Zack mail, as he is inspired by Zack's speech to the Shinra troops he commands.