While the Hulk is usually living proof that it's not easy being green, the recent debut of a new Yellow Hulk in Marvel Action: Avengers made quite a stir, and the character's first appearance is already blowing up on the secondary market. This new form is one of several variations of the classic Hulk, which also includes a Grey Hulk, Red Hulk, a Blue Hulk and other similar variations on the Green Goliath.
Perhaps the darkest and most misunderstood of these personas is the Devil Hulk, Marvel's first yellow Hulk, who also has a reptilian appearance and misanthropically genocidal tendencies, which made him one of the classic Hulk's greatest enemies. The Devil Hulk has recently returned in one of Marvel's most critically acclaimed ongoing titles, Al Ewing and Joe Bennett's The Immortal Hulk. While his intentions haven't changed, his relationship with Banner most definitely has.
The Devil Hulk first appeared in Paul Jenkins, Ron Garney and Sal Buscema's The Incredible Hulk #13 in 2000, and he was one of a myriad of different personalities within Bruce Banner's fractured mind. This particular personality is the manifestation of Banner's hatred and resentment toward the world at large for how it treated him, as well as his own negative feelings over being such a destructive monster. When first encountered, the Devil Hulk was psychologically chained up, but still free to voice his intentions to Banner as he traversed his own consciousness. However, Devil Hulk threatens to take over Banner's ailing body, using it to ravage the world that had given the Hulk such contempt beforehand.
Devil Hulk's appearance, though somewhat subject to change due to his psychological nature, was that of a gigantic, yellow, reptilian Hulk with immensely grinning mandibles. This demonic appearance and name matched the inner hatred and dark desires that Banner had always had toward humanity, and his realization of how deep these desires went made the threat even more pertinent. Things became worse when Devil Hulk was able to escape his chains, subduing Banner by trapping the rest of his mind in a fantasy world free of the nightmare that his life had become. Thankfully, Savage Hulk, Joe Fixit, and the Professor Hulk are able to break through the illusion. With his physical body recovering from Lou Gehrig's Disease, Banner and the Hulks imprison Devil Hulk once again.
Devil Hulk went unseen for years, all while new personalities such as the Green Scar -- the hero of Planet Hulk -- were introduced. The vilest Hulk persona would finally reappear, however, in the pages of Immortal Hulk, where he's become more of a threat than ever by hiding in plain sight. The series had resurrected the supposedly dead Bruce Banner, who now became the Hulk at night, much like his original Grey Hulk transformation. This new "Immortal Hulk" was actually the Devil Hulk, who was revealed to be connected somehow to the supremely evil and immensely powerful One-Below-All. The Devil Hulk had taken advantage of Banner's death and kept the other personalities at bay, which allowed him to make himself the dominant Hulk persona.
It's explained that Devil Hulk was never truly the outright villain that Banner had interpreted him as. In fact, he was something of a protective father figure to Banner against the oppressive treatment that the world had given him. His demonic form was simply a reflection of Banner's own distrust of said male authority due to the abuse that he had experienced from his biological father.
Despite his claims, Devil's Hulk goals remain the same, as all of his actions are meant to bring about the end of the human world. To this end, he enlists the help of other gamma mutates, as well as the remains of Shadow Base, to force his vision upon the Earth. In the end, Devil Hulk hopes to actually save both the planet and a remnant of humanity by destroying the majority of it, all the while harboring a defensive relationship over Banner. Though his environmental views and fatherly love for Banner are commendable, everything else about the anti-villain that could bring hell on Earth for the Marvel Universe.