An English one can be John Smith who was important for the establishing of Jamestown. He is famous because of the stories of Pocahontas but the stories were romanticized and he was a rather bad person in real life. Jamestown became the first serious colony of the British Empire.
A famous Dutch explorer is Adriaen Block. He was the person who managed to explore the New York area but at the time it was considered to be New Amsterdam. Thanks to his exploration, New Netherlands were established in the are and he named the islands around it.
A Spanish explorer can be Hernan Cortez. He was a famous conquistador who conquered the Aztecs in what is now Mexico and the land remained a Spanish colony in the time that came. That is why Spanish is spoken in Mexico today.
Samuel de Champlain can be the French explorer. He found New France and Quebec in the area that is nowadays Canada. He is popularly called the Father of New France because of that. He was the first person to make an accurate map of the area and the coast.