It seems as if this question wants a black or white answer, when the true answer can only be grey. There of course will be arguments that Columbus was a hero and that's why we celebrate Columbus Day. There will of course also be arguments that he was the first of many European villains who deliberately exploited then destroyed Native populations. It is my personal belief that both arguments are unfair to Columbus.
What Columbus did by sailing to America in search for a passage to India was inevitable. The social/technological progress that has characterized humanity for all time meant that the large dispersement of peoples and cultures across the world would be eventually bridged. Columbus just happens to be the figure in history responsible for the first official instance of Europeans coming into direct contact with Native Americans. Judging Columbus for the hundreds of years of disease and exploitation, thereby classifying him as simply a villain to humanity, is in realty too harsh a judgement.
Contemporary historians would do well to resist casting strict judgment on the figures of history and their deeds. Life was much different in Columbus' period, with morality and laws of society not as well established or matured as in the current period. What we know of what Columbus did in his own personal life is nothing truly out of the ordinary for his time period in terms of his behavior in relation to strange lands/peoples/cultures he did not expect to find. He simply was a product of his time, like all people of all times, like us. Hence the grey nature of this question's answer.
In summary, Columbus was neither simply hero nor villain. He was the first in a long line of people who would bridge the gap between cultures. The eventual rise of powerful nations, and the eventual fall of native populations, are of little consequence to Columbus personally. It's the differences in human opinion, both in Columbus' time and our time, that make this question impossible to reasonably answer any other way.
Think about what your essay will look like and which idea you favor; is he a hero or villain? I would make two lists, one for each idea and list which material fits under which column. That will help you form paragraphs for your essay. Now, the real question is which do you believe? I see Columbus as a hero for what he did and a villain for what he brought. As a hero, he sailed for Spain to find India and found a new world. The very act of sailing that far when he didn't know what he would find yet was courageous enough to sail anyway is amazing in that time. To Spain, he was a hero for bringing new treasure to Spain which helped fund more exploration. On the other hand, Columbus brought disease to the native people, usurped the native people's place in their own land, took whatever he could find for wealth back to Spain for its treasury, and in general, disrupted the lives of any people living where he landed. He was a catastrophic leader whose discoveries of new lands led to the destruction of many native peoples, their customs and their lives. His legacy lives on in the American Indians today who are marginalized in their own land. Even the name Indian is because Columbus thought he had landed in India.