A conquistador is a person who is out to conquer new territory.
A conquistador was the name given to the Fifteenth-to-Seventeenth century Spanish and Portugese soldiers who conquered much of the world, most famously the Central and Southern Americas. Not nice guys, but effective, and the term is still used today to describe certain people — ruthless business types, etc — who are brutally efficient at what they do. The most famous conquistador was the Spanish adventurer, Hernando Cortes, who subdued the mighty Aztec Empire of Mexico. The word comes, not surprisingly, from the Spanish verb conquistar, "to conquer."