We know extremely little about Sacajawea before she joined the Lewis and Clark Expedition. Sacajawea, whose name means "Bird Woman", was a Shoshoni woman probably born around 1788 or 1789. The Shoshoni (also spelled "Shoshone") were a large Native American group that spanned from southeastern California across central and eastern Nevada and northwestern Utah into southern Idaho and western Wyoming. Although the group comprised various different tribes, all Shoshoni spoke a similar language. Sacajawea's tribe was the Northern Shoshoni, and it dwelled in present-day Idaho. She spent much of her youth moving around the mountainous regions of Idaho and Montana, and she knew these regions very well.

As a young girl, Sacajawea was alone with some other women and children from her tribe when they were attacked by a war party from an enemy tribe, the Hidatsa. Sacajawea tried to flee into a nearby stream, but was captured. Sacajawea lived essentially as a slave under the Hidatsas, although she probably did not receive excessively harsh treatment. Then, when she was twelve years old, sometime around the turn of the century (1800), a French-Canadian fur- trader and trapper named Toussaint Charbonneau got possession of her. Charbonneau either traded for her or won her in a game of cards. Charbonneau made the young Sacajawea his wife, although he already had another wife, a Mandan woman named Otter Woman.

Charbonneau had lived in the frontier regions for years, working for the Montreal based North West Fur Company before working for himself. He hated civilized areas, even small towns. Considered something of a scoundrel and an incompetent by some, he preferred the wilderness, where he was free from civilization and free to chase Indian girls. Charbonneau lived among the Hidatsa, with whom he could communicate in a crude sign language. Although they sometimes made fun of him, the Hidatsa got along fairly well with the trapper, and Charbonneau was skilled enough in his sign language to communicate with various other Indian groups and serve as a sort of translator.

Sacajawea and Charbonneau weren't married by any formal ceremony, but they lived together and had children. Many trappers and traders of the frontier considered Indian wives highly desirable, so these types of relationships proliferated.

The facts of Sacajawea's life have provoked much disagreement, and the debates have only increased as she has gained more attention for her role as a female Native American hero. Even the correct spelling of her name has sparked contention, and various groups are now lobbying for what they believe is the "correct" spelling. During the Lewis and Clark Expedition, her name was spelled in a wide variety of ways (Lewis and Clark were creative spellers). Most often, her name was spelled "Sacagawea" in these men's accounts, and that was probably close to how her name was pronounced. Today, some Hidatsa Native Americans argue "Sakakawea" is a more accurate spelling, following the conventions for spelling that region's Native people's words in the English alphabet. The spelling that has perhaps the least real merit of all is the spelling used here, "Sacajawea". The author of the earliest account of the Lewis and Clark Expedition, although he had never heard the actual woman pronounce her name, decided to spell it "Sacajawea" simply because he thought it looked better. As a result, the majority of novels and historical biographies written about Sacajawea use the "j" spelling. Most texts today use this spelling, although a movement to change it to "Sacagawea," almost certainly a more accurate phonetic spelling, is now underway.

During her youth among the Shoshoni and the Hidatsa, Sacajawea learned much that would later enable her to help the Lewis and Clark Expedition. For instance, she became an expert in the local flora, becoming skilled at finding berries and nuts, a skill that would help feed the expedition and diversify its diet. Perhaps most importantly, her early capture by enemies accustomed her to hardship; somehow, Sacajawea managed to develop into a cheerful person who accepted the most difficult situations calmly. For this reason, she would practically never complain during the expedition, despite carrying a baby on her back on an 8,000-mile trek, a grueling journey that led even rugged frontiersmen into ill health and exhaustion.

Charbonneau, a rough-hewn trader and trapper, was apparently quite the colorful frontier character. The Hidatsas he traded with mockingly called him "Chief of the Little Village" and "Great Horse from Afar," names they considered quite hilarious when applied to Charbonneau--he must have cut a far less majestic figure. But if he understood he was the subject of Hidatsa fun, Charbonneau reacted good-naturedly, and seemingly never resented the Indians: he was constantly collecting new Indian wives throughout his 80-year life.

Sacajawea seems to have retained a cheerful attitude toward situations one would otherwise consider sources of discomfort or grief. For example, we might suspect that Sacajawea would begrudge being sold to Charbonneau and made into his wife. However, she accepted the situation happily and never tried to run away from her husband. This may be because life with a white man presented her with a better standard of living: indeed, Native American girls of this region and time often desired to marry white traders and trappers, whose money and access to towns and technology offered them amenities they had never enjoyed at home. However, there is evidence that Sacajawea's devotion to her husband extended beyond such motivations: indeed, she stayed with Charbonneau even though he sometimes treated her quite harshly. (One time during the expedition, Clark had to stop Charbonneau from hitting her, a fact that suggests the possibility of earlier physical abuse before the expedition.) We might also expect Sacajawea to have suffered under the extremely difficult conditions of the expedition. However, life had always been very hard for the Shoshoni and Hidatsa, especially during the winter, when they had little to eat and often came close to starvation. Thus although the Lewis and Clark expedition seems to have presented much hardship for its participants, Sacajawea had grown up under such hardship. Perhaps this helps to explain her cheerful attitude throughout the trip.