Krizalid is a high ranking agent of NESTS and the boss of the KOF 1999 Tournement. He was designed to be the ultimate Kyo Kusanagi clone. He was actually cloned directly from K' so he has his memories and also believes Whip to be his sister.
Krizalid wears a sophisticated battle suit designed to feed battle data on the various fighters to NESTS Kyo clone army. Krizalid challenges the winning team to gain the data necessary to accomplish this feat. Upon his defeat by the hero team the Kyo clones are neutralized and Krizalid is killed by his superiors for his failure.
Krizalid's body is later recovered and revived by Zero. Krizalid returns in the 2001 tournement allied with Zero. They face off against the hero team and are again defeated. Krizalid is killed once again during the encounter.
King of Fighters XIV
When Verse is defeated Krizalid is one of the souls shown to be restored to life.