Vikings is a broad term that is commonly applied to the Germanic tribes that inhabited the Scandinavian regions during the latter years of the Roman Empire. As the Empire began to break up, these tribes began to invade areas abandoned by the retreating Romans.
Although generally all called Vikings, not all Vikings were the same. Saxons, Danes, Norsemen, and Normen, all roamed Scandinavia, Normandy, and the Northern Seas. Most made a living of pillaging, leading to many of the stereotypes: bloodthirsty barbarians, conical helmets often with horns. Most of these stereotypes came from the Norwegian Norsemen tribes, and from the two most famous of Vikings Eric the Red, and his son Lief Erricson.
Eric the Red is credited with the discovery and colonization of Iceland. Lief Erricson is credited with the discovery of Greenland, and a place called "Vinland" which some historians speculate may have been North America.