In the debut, Lee chose Grey for the Hulk because he wanted a color that did not suggest any particular ethnic group. Colorist Stan Goldberg, however, had problems with the grey coloring, resulting in different shades of grey, and even green, in the issue. After seeing the first published issue, Lee chose to change the skin color to green. Green was used in retelling of the origin, with even reprints of the original story being recolored for the next two decades, until The Incredible Hulk vol. 2, #302 (December 1984) reintroduced the Grey Hulk in flashbacks set close to the origin story. Since then, reprints of the first issue have displayed the original Grey coloring, with the fictional canon specifying that the Hulk's skin had initially been Grey.
The Hulk possesses the potential for limitless physical strength depending directly on his emotional state, particularly his anger. This has been reflected in the repeated comment, "The madder Hulk gets, the stronger Hulk gets." After probing, the entity Beyonder once claimed that the Hulk's potential strength had "no finite element inside. His durability, regeneration, and endurance also increase in proportion to his temper. Greg Pak described the Hulk shown during World War Hulk as having a level of physical power where "Hulk was stronger than any mortal—and most immortals—who ever walked the Earth."