Darkness and Light: Part 1 - S1-E11
Stupidity: When the Leader's spy is reporting to him, he removes his human mask for the benefit of the audience. This is a pretty foolish thing to do considering he's in a top secret military base, where he can be seen by anyone that happens to be in the area, or potentially by security cameras.
Answer: The Hulk is a giant brute who smashes everything in his path when he is angry. In Ang Lee's "Hulk," General Ross, played by Sam Elliot, explains it to his daughter.