Kluh is a Marvel comics supervillain and one of several malicious alter-egoes of the Hulk - described as the "Hulk's Hulk" he shares many similarities with both the Devil Hulk and Guilt Hulk, but is considered a fully independent entity. While the Hulk is largely heroic when not provoked, Kluh is a vicious and evil-minded beast ruled by hate and distinguished from other Hulk alter-egoes by his black skin, glowing red scars, and equally demonic eyes - his hair also turns white and his hands become more akin to talons.
Kluh, in fact, is born of Hulk's own rage and is repressed by Hulk as such - this shows how dangerous Kluh is, since even during World War Hulk, the Hulk would have been fighting off Kluh's influence in order to stop the monster emerging. During the AXIS storyline, however, Hulk was unable to stop Kluh from emerging and the monster took control, he quickly showed his power as he decimated the Avengers with ease.
Kluh retains most of Hulk's superhuman strength, regenerative healing abilities, and indestructibility, as well as his claws, which, coupled with his own muscles, could add to his deadly arsenal of powers. Compared to the Hulk, who is occasionally destructive and violent in his battles, but nevertheless remains the hero we know him to be today, Kluh literally serves as his polar opposite, fitting due to the AXIS storyline centering on the heroes and villains having their moralities switched.
Kluh is sadistic, merciless, unpleasant, and destructive, wanting nothing more than to cause senseless destruction, and "bathe in the blood of the innocents". This also proves he is cruel, bloodthirsty, aggressive, heartless, violent, and egotistical, and is just one primary example of how dangerous and unpredictable Kluh is. As if that wasn't enough, even the inverted Avengers were alert about him and the present danger he poses, regardless of which side he is on. He also has shown to be quite a cannibal, as he attempted to eat off Nova (Sam Alexander)'s arm with no sign of regret or hesitation, even though Nova technically is still just a young kid. Twisted, callous, arrogant, monstrous, immoral, and deranged, Kluh is one of the evilest alter-egos of the Hulk, and it is no wonder why so. It was only after the White Skull, or the inverted Red Skull, with the help of Dr. Doom, Scarlet Witch, Brother Voodoo, and Captain Steve Rogers, that Kluh was wiped away from the face of the Earth, and the Hulk is rendered back to normal, along with the other heroes and villains.