Neytiri

Neytiri finds Jake alone in the forest, saves his life and, reluctantly, takes him to the clan. She teaches him to hunt, to ride and to listen to Eywa. When Jake reveals he was spying for the RDA, she feels betrayed. After Hometree falls, where her father dies, she fights beside him in the final battle and kills Quaritch to save him.

Years later, Neytiri is mother to four children and lives with Jake among the Omaticaya. She flees with the family to the Metkayina and finds the sea strange, but works hard to protect her kids. In Quaritch's attack, she and Jake go after Kiri and Tuk, and Neytiri even threatens to kill Spider to make him release her daughter. Neteyam's death marks her for good.

After her son's death, Neytiri's hatred of humans grows and she doesn't want Spider around. On the merchant-ship trip she gets separated from the family and has to fight her way back. She infiltrates the RDA base and, in the Tulkun battle, delivers Ronal's daughter before being captured. Varang tries to kill her, but Kiri saves her.

Zoe Saldaña plays Neytiri in all three films. Per Wikipedia, Cameron considered Q'orianka Kilcher before casting her, and Saldaña helped screen-test the actors vying for Jake, including her future co-star Sam Worthington.