Nali was originaly a high captain in the Ta-Koro Gaurd. On a mission though, he killed two of his best friends (Or so he thinks) and severly injured Flam. This was because Inffessted Terran promised him wealth and power. Inffessted then pushed Nali and Flam into the Mangai volcano. lucky for them, flam hit a toa stone on the way down and they were both turned into four armed cyborgs.
Now Nali is a soldier in the Ak-Ri-An air force serving under Kav. He has power over ice and absorbtion(black holes). He created a black hole which ended up destroying a small part of Blackwave. He also has a BIG grudge against Flam and Infessted