They are, genetically speaking, our closest relatives in the animal kingdom. Most of them have opposable thumbs and have learned to use tools, or at the very least, some level of problem solving skills. By watching them we have made suppositions about the earliest forms of man, including how we hunted and lived before we were able to think up logical solutions to solve our housing dilemma. Monkeys have offered us all of these insights into our past and have also shown us, through exhibitions and other forms of training from their human counterparts, we may have evolved into the beings that we are today.
For generations man has tried to learn what we may have been like millennia ago from studying the processes a monkey or ape would go through to solve a problem. Through these studies we have come to find out that, while super intelligent on an animal scale, monkeys are not all created equal on the intelligence front. However, despite the decades of research, scientists have been unable to even hypothesize the link between primates and humans until very recently.
With the discovery of the several missing links in the last decade there have been ever more and ever changing, with new information gathered from fossil records, hypotheses as to how humans evolved from chimps. The missing links also close the door that was open to creationists for decades by proving that Chimpanzees aren’t just there, they were part of something larger at one time.