Christopher Columbus set out for a goal, obtained backing and had a significant impact on our world today
True, there were people already living in the Americas, and Christopher Columbus may have landed in the New World by accident, but that does not change the fact that his "discovery" changed human history immeasurably.
In Christopher Columbus' day, it was considered that you would fall off the end of the earth if you sailed too far. He overcame this misconception and tried to sail to India, believing the world to be round and not flat. In doing so, he accidentally put the continent of America on the map.
Without any of the modern advantages, Christopher Columbus discovered the new world.
Columbus really opened up the 'New World' and started a new era in modern history
Captain James Cook was the first to set out with the deliberate aim of not only discovering land, but plants and animals as well. A great cartographer and sailor and leader of his men.
As well as travelling to places unknown to Western civilisation, Captain James Cook kept impeccable records and charts of his discoveries.
Colin Taylor, USA
Other explorers have walked, sailed or flown to various uncharted parts of the globe, but in billions of years of evolution Neil Armstrong was the earth-born creature to set foot on another planet.
Paul Coombs, UK
Together with the rest of the early astronauts in both the USA and the USSR, Neil Armstrong opened the door to the rest of the universe, now that the age of exploration on our own planet is coming to an end.
Marco Polo was one of the first people to sail to India and China and, most important, to bring back a lot of information on their culture.
André Leroux, Canada
Marco Polo's trip of discovery was one that had some possibility of success but the greater likelihood of no return.
Ernest Shackleton had supreme courage, mental and physical toughness, and leadership qualities.
George Spearing, New Zealand
Being great in anything is more than what someone achieves, but also what kind of person achieves that greatness. Sir Ernest Shackleton certainly was a great man of character, resolve, and leadership; a man that epitomised the greatness of the human spirit.