One major similarity between Jack in Lord of the Flies and Adolf Hitler is how both use violence, fear, and intimidation as a means to gain and keep power. Jack's ability to kill and gut the sow impresses the other boys on the island; they perceive him as both a warrior and provider. After Jack uses violence to steal Piggy's glasses, he leads the other boys away, "trotting steadily, exulting in his achievement. He was a chief now in truth; and he made stabbing motions with his spear" (168).
The other boys value Jack for his ability to use violence against the pigs, and in this case, to secure Piggy's glasses by use of force. Jack also intimidates the other boys into cooperation, sometimes by use of force, in the case of Samneric, who claim that they joined Jack's tribe because "they made us. They hurt us--" (188).
Hitler also used violence and terror to control. With the backing of the SS, Hitler carried out acts of violence, such as "The Night of the Long Knives" and "Kristallnacht," against his political opponents and others who would oppose him. Like Hitler, Jack also used terror to control. Even though Samneric feel more allegiance to Ralph, they do not dare to go against Jack and his henchman Roger.
Perhaps it's the passage of time, but the true nature and history of Adolf Hitler and of the regime he ruled have been increasingly marginalized in the rush to compare other personalities to his. That is a shame, because the crimes of which Hitler was guilty defy easy comprehension and were so vast and horrible in scale that any comparison, except, perhaps, to Joseph Stalin, Mao Zedong, and Pol Pot, does damage to the memory of those who perished under Hitler's rule.
In William Golding's novel Lord of the Flies, the character of Jack represents the dark side of humanity. Unlike Ralph and Piggy, who deliberately seek to retain a sense of humanity, Jack and his followers quickly descend to the most vile, basic instincts of man. Jack becomes consumed with blood lust and leads his faction among the young boys in creating a violent tribal environment. When the effort to hunt down the pig and consume its meat becomes an obsession, he cries out in primal enthusiasm, "Kill the pig. Cut her throat. Spill her blood." In Chapter 5, Ralph and Piggy discuss their concerns about Jack and how the latter holds dangerous grudges against them for their role in controlling the fire and for the simple fact of their refusal to join Jack's group. Jack, in short, is a bad boy. He is capable of anything, and the boys with Ralph know it.
So it is established that Jack represents the dark side of man. Does that equate him, a twelve-year-old boy stranded on an island, with the most reprehensible figure in history? Probably not. Jack's circumstances and his youth clearly separate him from an adult who knowingly conceptualizes a theory of racial superiority, who maneuvers himself to the top of a government, and who proceeds to carry out the greatest crime against humanity in history. To the extent that Jack can be considered a microcosm of Hitler, even that comparison is weak. Again, the circumstances surrounding Hitler's rise to power, in the most technologically advanced nation in Europe, and the circumstances surrounding Jack's descent into inhumanity are so disparate that, again, the comparison is seriously weak. Yes, Jack creates a dysfunctional and brutal environment; no, he is not Hitler.