Let's talk about the Immortal Hulk!
The Immortal Hulk was recently revealed to be the "Devil Hulk" who was first introduced in Paul Jenkins run back in the early 2000s. He looked like this:
This Hulk obviously doesn't look like the one we see in Immortal Hulk because this is how Banner saw him in his own mind. Devil Hulk represented the culmination of Bruce's hatred for the world and his own guilt. Jenkins also explored the hell out of Banner's split personality disorder and dissected what each Hulk meant to Banner.
Savage Hulk represented Banner's childhood, a screaming dummy who just wanted to be left alone due to the abuse he received under his father.
Joe Fixit the Grey Hulk represented Bruce's teenage years (where he....wanted to be a gangster I guess? That one isn't explored too well)
"The Professor" aka smart Hulk represented Banner's adult years. It was revealed during this run that Smart Hulk wasn't actually even Banner but another personality that THOUGHT it was Banner.
Jenkins also introduced the idea that there are thousands of Hulks in Banners mind, just waiting to be unleashed. One of these is a Clown Hulk.
Also, one time during Peter David's run, the "Smart Hulk" decided to become a baseball player by doing blackface: