When the Hulk was first conceived of, Stan Lee decided to make the Hulk gray in color because he didn’t want to imply any specific ethnic group. So for the first few issues the Hulk was varying shades of gray and even a gray green. This is because at the time coloring technology at the printers was unable to consistently reproduce a good gray color. Eventually Lee gave into arguments and just made the Hulk green, a much easier color to reproduce. Also in the early comic book series, Dr. Bruce Banner changed into the Hulk as sunset.
It wasn’t until later that he only changed into the Hulk when he became panicked or angry. The Hulk has a love interest in Betty, the daughter of General Thaddeus Ross. Betty tries endlessly to stop her father’s endless mission to find the Hulk and catch or destroy him. In later issues of the Hulk series Betty is killed off, causing a rehabilitated Hulk to turn into a rampaging destructive force.
The original Hulk comic book was cancelled after six issues, but the Hulk has continued on in many forms. He’s had running guest appearances in other comics, he’s had new comics of his own, including the long running, The Incredible Hulk comic, a cartoon series, a live action television show, and movies. So the Hulk has had a long running success.