We almost saw the origin of a major supervillain but he disappeared due to a side mission of Black Widow
Marvel’s 2008 movie The Incredible Hulk, was a promising movie but it wasn’t explored further afterwards. Hulk didn’t get his solo movie series and instead became part of the Avengers and Thor: Ragnarok, where we found Banner finding love in Natasha Romanoff, aka, Black Widow, and in the five years between Avengers: Infinity War and Avengers: Endgame, we saw him transition into Professor Hulk, where he got to bring the man and the monster together.
But because his own story wasn’t further explored, we didn’t get to see some of Hulk’s biggest enemies on screen, such as The Leader, who played a supporting role in The Incredible Hulk as scientist Samuel Sterns or Mr. Blue. Towards the end, we see Sterns getting exposed to Banner’s gamma infused blood and slowly transitioning into his villanous self, but he wasn’t shown afterwards.
What happened to The Leader?
Him not showing up in the movies was never explained but in the comic book series, Marvel’s The Avengers Prelude: Fury’s Big Week, we get to see what really happened. In that, Black Widow was able to neutralise him before he became a greater threat.
Before Natasha’s mission on Tony Stark, she had been sent with other agents to track Banner’s movements. Assuming the guise of a university student, Romanoff infiltrated Culver University at the time he Hulked out and fought General Ross’s army. She got to see Emil Blonsky’s enhanced strength and speed and instead of getting involved in the fight, she went to Sterns’ lab and saw him mutating into a creature with a massive brain.
Sterns was able to deduce Natasha’s place of origin from the faint traces of her Russian accent, and tried recruiting him, but she shoots him in the leg and calls a SHIELD cleanup crew. Sterns is then placed in a submerged tank in a sedated state and his career ended before it could begin.