Iori Yagami is the heir of the third clan that sealed the ancient entity known as Orochi, with the uses of sacred treasures. The three clans are the Kusanagi, Yata, and the Yasakani clan, (Which is now known as the Yagami clan).
In the ancient history before the King of Fighters series takes place, the seal of Orochi begins to weaken. The three clans begin to move to another location in hope to strengthen the seal again. One day a member of the Hakkesshu, followers of Orochi and hopes to have the three clans to turn against each other, killed a member of the Yasakani's clan and framed the Kusanagi's for the crime. The Hakkesshu then approached the head of the Yasakani clan and made a pact with Orochi for the power to defeat their (now) enemies. However the blood pact with Orochi came with a curse, the woman of the Yagami clan will die at the brith of the first child, and the male will die young.
Following the 1994 tournament, Iori decided to enter the following years contest as part of the Rival Team with Billy Kane and Eiji Kisaragi . Iori was on a personal mission to kill his rival, Kyo Kusanagi. Iori fails to make it to the finals that year and turns on his teammates enraging the two men who swear vengeance.
In 96' Iori forms a team with Mature and Vice, the former secretaries of Rugal Burnstein. Mature and VIce are secretly members of the Hakkesshu and are there at the behest of Goenitz who is seeking to revive Orochi.
The host of the 96' tournament, Chizuru Kagura, is one of the Three Sacred Treasures and has brought Kyo and Iori together in the hopes of preventing Orochi's return. Goenitz looses to the trio and calls out ot Mature and VIce who turn their back on the leader of the Hakkesshu. As a last act before he dies, Goenitz activates the "Riot of Blood" within Iori and the young man turns into a savage beast and kills his teammates.
The following year the Three Sacred Treasures are present when the New Faces Team sacrifice themselves to bring Orochi back to the earthly plane. Orochi activates the Riot of Blood turning Iori into Wild Iori in the hopes that he would kill his teammates as he did the previous year. However Iori managed to retain enough control to hold Orochi so that he could be sealed away by Kyo and Chizuru.
Tales of Ash
Chizuru hosts the 2003 tournament and reforms the Sacred Treasures team to investigate the weakening of the Orochi seal. Ash steals the Yata Mirror from Chizuru and tells Iori that he is next.
In KOF XI Iori teams with Kyo and Shingo Yabuki. At the end of the tournament Iori loses control and attacks his teammates. Ash Crimson attacks him and steals his treasure/power.
In the KOF XIII a powerless Iori is teaming with a returned Mature and Vice. After Saiki and Ash are erased from time, Iori is given the choice to give him his treasure and be free of the Orochi curse. Iori decides to have his powers restored upon which Vice and Mature disappear once again.
Iori once more teams with Mature and Vice. Upon Verse's defeat he travels to Hungary with the Sacred Treasures to reseal a weakened Orochi.