Freydis Eriksdottir
Whilst Leif was the spitting image of the perfect American Child, Freydis was just like her father except that she was probably insane. When her husband, Thorvard, lead an expedition to Vinland this was especially evident. Thorvard and his men had brought a cow with them, and traded its milk with the natives. They were all lactose intolerant, as they didn't have the gene responsible for the production of lactase in their intestines and thought that the strangers had poisoned them. They promptly attacked the viking camp.
"Then Karlsefni and Snorri see that the Skrælingar are bringing up poles, with a very large ball attached to each, to be compared in size to a sheep's stomach, dark in colour; and these flew over Karlsefni's company towards the land, and when they came down they struck the ground with a hideous noise. This produced great terror in Karlsefni and his company, so that their only impulse was to retreat up the country along the river, because it seemed as if crowds of Skrælingar were driving at them from all sides. And they stopped not until they came to certain crags. There they offered them stern resistance.
Freydis came out and saw how they were retreating. She called out, "Why run you away from such worthless creatures, stout men that ye are, when, as seems to me likely, you might slaughter them like so many cattle? Let me but have a weapon, I think I could fight better than any of you." They gave no heed to what she said. Freydis endeavoured to accompany them, still she soon lagged behind, because she was not well; she went after them into the wood, and the Skrælingar directed their pursuit after her. She came upon a dead man; Thorbrand, Snorri's son, with a flat stone fixed in his head; his sword lay beside him, so she took it up and prepared to defend herself therewith.
Then came the Skrælingar upon her. She let down her sark and struck her breast with the naked sword. At this they were frightened, rushed off to their boats, and fled away."
-The Saga of Erik the Red
Freydis's apparent insanity wasn't just good for driving off angry Vinlanders, it was also a great danger to her fellow northmen. When she, her husband, and his crew were camping at a Norse outpost for the winter she made several actions that lead to serious consequences. One night, she marched into a boat captain's cabin and demanded that he give her his boat. Of course, the captain did what any viking would do and beat her up. She immediately returned to her husband and demanded that he go and kill the other captain and his crew, which he reluctantly agreed to. By morning, the other crew was dead, leaving only their wives. Freydis promptly took her husband's axe and murdered them as well.