The Leader is the polar opposite of the Hulk. He’s super intelligent or at least he was until General Thaddeus E. “Thunderbolt” Ross AKA Red Hulk absorbed his Gamma radiation and depowered him. Now he’s like the rest of us. He has to rely on the internet, literally. The Leader uploaded backup brains!
The Leader is forced to to join Ross’ self-serving superhero team, the Thunderbolts, but the former supervillain bides his time. He seizes his opportunity during a mission to real-life Temple of Doom in Thunderbolts #26 by writer Charles Soule.
The temple has booby traps that he uses on all his teammates including Deadpool, a crazy superhero who thinks he’s a comic book character. The Leader tells him to step on stone that triggers a trapdoor to a lava pit but he doesn’t fall for it. Deadpool explains that everyone assumes he’s dumb because he’s fun.
“And you know what they say about people who assume things… I stab them,” he says with a demonstration. “‘Assume something, and Deadpool will stab you.’ That’s what they say.”
Nevertheless, he still dies. The Leader triggers the trap himself. With his dying breath the Merc with a Mouth simply gives him the middle finger like end scene in the Terminator 2.
At the center of the temple the Leader drinks the blood from the head of a dead god known as a Celestial. It makes him smart… too smart. His over-sized brain grows even larger until his head explodes.
Of course, you don’t need to be a genius to know Marvel isn’t about to kill off so many characters.
The Red Hulk is confronted by a normal man who drank the blood and therefore not overloaded. He offers the sole survivor of the team a chance to go back in time and be less self-serving. Ross accepts the offer and nixes the mission before ever taking it.