IIRC, we saw Samuel Sterns in the 2008 film, but when he was becoming the Leader, he went off screen and didn't see him again, giving me the impression (at the time) that there'd be a sequel with him shown as the Leader, but it never happened. Is it still possible we could get another Incredible Hulk movie, which might also show the Leader?
The problem with a Hulk movie is the essential problem with the Hulk character that many Hulk fans refuse to tackle. Anger is usually a bad thing. If you see someone get angry in public, your first response is to get away from that person. When Hulk gets angry in comics, it’s fine when he’s tackling a supervillain; but often, Hulk’s anger in the comics is represented as a rampage. Yes, he’s misunderstood, but he’s also a very huge threat, and in the real world, no one would stand for a real Hulk being allowed to exist. This has been an aspect of Hulk’s character from the beginning. He’s a tragic Jeckyll and Hyde character. Banner dreaded turning into the Hulk and sought a cure from the Hulk. But the primary appeal of the Hulk to many of his fans is just how powerful he is. They enjoy the Hulk most when he is most unleashed, meaning when he is most angry, when he’s most lashing out. Basically, they enjoy the tragedy, which is the ugliness of anger.
This puts Hulk fans and movie makers in a dilemma. Anger shouldn’t be celebrated, and doing so turns off many people. Banner represents the anti-anger side of the character, which is why he is necessary. But the pro-anger side sees Banner as boring. They don’t want the Hulk controlled. That’s the very point of anger and the point of the Hulk. It’s a power fantasy about lashing out in all the ways you can’t in real life. But a truly mature understanding of this dynamic is to acknowledge that there are very good reasons why you can’t lash out and why you should control your anger.
A solo Hulk movie struggles with this whereas an Avengers movie doesn’t. An Avengers movie barely touches on this struggle and allows the Hulk’s anger to be directed when it’s time for him to shine. When Hulk is just another player, he can stand out without the focus on the more problematic aspects of his character because there are all these other characters and their arcs to distract you from Hulk’s.