The spread of Hellenistic culture, the culture of the Greeks, was caused by a Macedonian. Alexander the Great was taught Greek Culture and Macedonian battle from a young age. His father, Philip, took a hardy and tough people and turned them into the war machine of its age. With this came power and wealth, and he was able to send his son to study under the great minds of the time in Greece.
Learning never stopped for Alexander. He always wondered what was over the next hill. He brought with him on campaign scholars to chronicle not only his deeds, but the world he found. He set up cities, roads, and philosophies all along Greek lines wherever his feet trod.
His men loved him, and he had a genius for logistics. With these assets, he was able to conquer most of the known world. He set up cities along Greek lines, with Gymnasia and other institutions of learning and Greek culture. He then populated these cities with retired soldiers, many Greek and Macedonian, who propagated this culture. He also married many of his men off to local women in mass ceremonies, tying them to the new land.
Upon his death, his generals split up his Empire, taking large sections for themselves. This stabilized the newly conquered area in a short amount of time, especially as Alexander had left the ruling structure in place whenever he was able to do so, so there was little uprising or change in the day to day life of the citizens.
Over a fairly short amount of time, the indigent people found how beneficial it was to take up a Greek lifestyle. New avenues were opened to trade, knowledge was freely passed, and health and sanitation were upgraded. Possibly most importantly, however, was the social opportunities. Parents were able to send their children to the Gymnasia to take classes on being Greek. After their graduation, they were considered to be Greek citizens, and even more opportunities opened up for them. This benefited both the Greeks, who got new blood and new ideas, and the indigent peoples, who broke down the walls of social stratification to a degree unheard of before.
Soon, all the people in Alexander's former empire thought of themselves as Greek. And while the Hellenistic era officially ends with the advent of the Roman Empire, the Romans are in many ways merely a continuation of this. The Romans themselves were Hellenistic, taking many of the best ideas and plans of the Greeks and putting them to use.
Without this spread of Hellenistic culture, our world would be a much different place. Two major religions, Judaism and Christianity, come from this culture and would not be as they are today without it. Hellenism gave the world a common language with which to trade ideas and items, which sped the growth of science and learning more than can be imagined.