Over 3,000 years ago, Kalos was in a war, AZ's Pokémon, a Floette, was forcibly recruited and died in the war. Heartbroken, AZ invented a machine that harnessed the powers of Yveltal/Xerneas, the legendary Pokemon of death/life, in order to give eternal life and bring the dead back to life, at the cost of draining the life energy of other beings. He used it to recover his Floette which in turn also made both of them immortal. However, he still was angry to the people for their greediness so he converted his machine a powerful weapon that drained the life of countless of Pokemon and killed almost every living being in an extremely big perimeter.
The destruction caused by the ultimate weapon ended the Kalos war and AZ became the new king of Kalos, but Floette abandoned him disappointed by the horrible actions her owner commited. Yveltal/Xerneas also died after having its energy drained by the machine and reverted into a coccoon-like form so it could come back to life eventually.
The massive amount of energy produced by the blast of the ultimate machine and the spirits of the thousands of dead Pokemon eventually led to the creation of both the Mega Evolution and the Infinity Energy. The remains of the dead Pokemon's spirits became rock structures scattered around the area where the ultimate weapon was built, which would eventually become Geosenge Town.
Overwhelmed by guilt, AZ spent thousands of years as a wanderer searching Floette while at the same time carrying the key to the machine hoping no one would ever turn it on again. In the modern ages, Lysandre reused the machine in an attempt kill all living beings except Team Flare to prevent overpopulation. He obtained the coccoon of Yveltal/Xerneas and kidnapped AZ in order to steal the key to the machine. The player character would find AZ imprisoned in Lysandre's lab, AZ warned about what would truly happen if Lysandre were to turn on the machine and begged the player to stop him from repeating the mistake that AZ once commited. The player's actions would cause Xerneas/Yveltal to come to life before the machine could fully charge and were then caught by the player. Lysandre attempted to use fire the ultimate weapon despite not being fully charged and due to the evacuation of the city, it didn't cause much damage except it apparently destroyed itself and seemingly killed Lysandre. AZ then thanked the player for destroying the machine once and for all.
After the protagonist defeated Diantha, AZ battled the player to find it out how it is to be a trainer. After it, he said that he regretted what he did and his Floette floats from the sky, revealing that it was watching him all the time.
Although not by name, AZ is mentioned several times during the Delta Episode of Pokémon Omega Ruby and Alpha Sapphire. He and his actions 3,000 years ago are first mentioned by Mr. Stone, who tells that his grandfather got the idea to use the same energy used by the ultimate weapon to improve the lives of people and Pokémon alike, thus leading to the creation of Infinity Energy, which the Devon Corporation used to grow into one of the top industries in Hoenn. Later, the player overhears Wallace talking with his master, learning that the tree planted in front of the entrance to the Cave of Origin was given to the people of Sootopolis by a "huge man who visited from the Kalos region." Underneath the tree there is a flower of the same kind as the one carried by AZ's beloved Floette. AZ is mentioned once more by Zinnia at the Sky Pillar, telling that "a tall visitor from a distant land" once witnessed how Mega Rayquaza stopped a fight between Primal Groudon and Kyogre, having said, "It is the Δ (Delta), born of the great disturbances in this world. By the bonds born of mankind's wish and the power of the stones, it will calm the troubles that plague the world."
- AZ is the tallest person in the main series games.
- He did not appear in anime.
- AZ is the oldest known human in the history of Pokémon, games or otherwise.
- All of the Pokémon that AZ uses in battle are Pokémon associated with ancient civilization or longevity; Torkoal is based on a tortoise, which can live for multiple centuries, and both Golurk and Sigilyph are Pokémon thought to be from ancient times. Also, all know Return, indicating a high friendship level with AZ.
- His name is from the letters A and Z, meaning the beginning and end.
- An interview with Junichi Masuda in Game Informer magazine reveals that AZ's Floette was given to him by his late mother and was taken by force by the soldiers fighting in the war.
- The interview also reveals that AZ's great height is due to the influence of the ultimate weapon's power on his body, and that he continued to age despite being immortal.