the genius of james cameron is that:
1.) he killed off all the ‘name’ stars in avatar (sigourney weaver, michelle rodriguez)
2.) he turned sam worthington, his leading man into a blue alien
3.) and his female lead, motion capture acted by zoe saldana is also a blue alien
so now, no actor can interfer with his making sequels (hold up and hold out for loads of money). he could recast his 2 leads and nobody would even notice.