Animal Farm is founded on the idea that humans are evil. Are humans truly evil? Explain how the human characters contribute to the novel's overall theme and the issues that arise from interacting with them. Also explore how the animals’ characters come to compare with that of humans? What is it in human nature that makes humans evil or good?

The humans are not truly evil, at least in the way that Napoleon claims. Animal Farm is founded based on the idea that animals are intrinsically better than the evil humans, but the story shows us that this is not the case.
When Animal Farm is initially founded, Napoleon, Snowball, and Squealer formulate a philosophy called Animalism, summarized by seven principles that the animals must adhere to. These principles are designed to make their behavior superior to that of the humans. As the plot unfolds, we see the pigs (especially Napoleon) begin to desire more power and privilege. They behave more and more like the humans as they disregard the seven principles. Eventually, the pigs have become so human-like in their behavior and dress that the other animals cannot tell a difference between the pigs and the humans.
The difference between the animal and the humans is not that animals are intrinsically better. It's the principles and behavior they choose to live by that makes the difference. With the pigs, we see that it is the desire for more power and privilege that leads them to make evil choices. This desire is what causes both human and animal characters to be evil.
Animalism is a communistic philosophy. One major theme of Animal Farm is to illustrate how Communism, even if it is well-intentioned, leads to greedy and evil men claiming power and privilege by oppressing others. This is clearly seen in the way the pigs become just like the humans in the story.

Humans are not truly evil. It is easier for Old Major, in encouraging the animals to dream of rebelling and taking over the farm for themselves, to paint humans as all evil. This sets up an "us against them" dichotomy, where the animals are cast as all good and the humans as wholly bad. While not true, it unifies the animals.
The chief human we learn details about is Farmer Jones. It appears he treated the animals decently until he fell into alcoholism. He is not truly evil, simply suffering from a disease (alcoholism) that causes him to neglect the animals.
Animal Farm challenges simple notions of one group being all good and another all evil. It shows that like humans, animals can be a mix of good and evil. The novel chiefly argues that it is too much power that corrupts both humans and animals. The pigs become like humans only because they have amassed too much power.