Antoine Laumet de La Mothe, sieur de Cadillac (1658 – 1730) was a French explorer and adventurer in New France, now an area of North America stretching from Eastern Canada in the north to Louisiana in the south. Rising from a modest beginning in Acadia in 1683 as an explorer, trapper, and a trader of alcohol and furs, he achieved various positions of political importance in the colony. He was the commander of Fort de Buade, modern day St. Ignace, Michigan, in 1694. In 1701, he founded Fort Pontchartrain du Détroit, the beginnings of modern Detroit, which he commanded until 1710. Between 1710 and 1716 he was the governor of Louisiana, although he did not arrive in that territory until 1713.

La Mothe was a controversial figure in New France. His knowledge of the coasts of New England and of the Great Lakes area was appreciated by Frontenac, governor of New France, and Pontchartrain, Secretary of State for the Navy. This earned him various favors, including the Order of Saint Louis from King Louis XIV. The Jesuits in Quebec, however, criticized his perceived perversion of the "Amerindians", North America's indigenous peoples, with his alcohol and fur trading. La Mothe was imprisoned for a few months in Quebec in 1704, and again in the Bastille on his return to France in 1717. His visionary spirit continued in the city he helped found, Detroit, which became the world center of automobile production in the 20th century. William H. Murphy and Henry M. Leland, founders of the Cadillac auto company, paid homage to him by adopting his name for their company and his armorial bearings as its emblem in 1902. Various places bear his name in North America, in particular Cadillac Mountain, Maine, and the town of Cadillac, Michigan.

Antoine was born "Antoine Laumet" on March 5, 1658, in the small town of Saint-Nicolas-de-la-Grave in the Tarn-et-Garonne département of France, in the Midi-Pyrénées région. His father, Jean Laumet, was born in the village of Caumont-sur-Garonne and became a lawyer in the Parliament of Toulouse. Jean was appointed lieutenant to the judge of Saint-Nicolas-de-la-Grave by Cardinal Mazarin in 1652, and later a judge himself in 1664. Antoine's mother, Jeanne Péchagut, was the daughter of a merchant and landowner.

La Mothe's adult correspondence reveals that his youth included rigorous study at a Jesuit establishment where he learned theology, the law, agriculture, botany and zoology. Upon his return to France from Louisiana, he asserted in his record of service in 1675 that he had enlisted as a cadet at the age of 17 in the Dampierre regiment, in Charleroi. Two years later in his letters, however, he reported that he was an officer in the Clérambault regiment in Thionville, and in 1682 he joined the Albret regiment, in Thionville. This part of his military service has not been confirmed. It may be the record of his older brother François, because it appears inconsistent with Antoine's academic level.

At the age of 25, Antoine Laumet departed from France to the New World. His father lost a lawsuit against a lawyer in Castelsarrasin that caused him financial difficulties; statutory forfeiture caused by the loss of his father's financial support following the death of Cardinal Mazarin; intolerance against Protestants. Laumet may have embarked on his voyage by devious means, as historians have not found an official list indicating his presence on a ship departing from a French port.

In 1683, Antoine Laumet arrived at Port Royal, the capital of Acadia. During the next four years, he explored his new country in all directions, extending his explorations to New England and New Holland, pushing on south to the Caroline, now North Carolina & South Carolina, and familiarizing himself with the native Indian languages and habits. He probably entered into a business relationship with Denis Guyon, a merchant of Quebec. On June 25, 1687, he married Guyon’s daughter, Marie-Thérèse, 17, in Quebec. The marriage certificate is the first document where his new identity appeared. He called himself "Antoine de Lamothe, écuyer, sieur de Cadillac", and signed as "De Lamothe Launay". In fact, like many immigrants, he took advantage of his arrival in the New World to create a new identity, perhaps to conceal the reasons that drove him from France. This new identity "ne sort pas de son sac" ("I did not create this identity out of nowhere"), as he wrote later. Antoine Laumet likely remembered Sylvestre d'Esparbes de Lussan de Gout, baron of Lamothe-Bardigues, lord of Cadillac, Launay and Le Moutet; adviser to the Parliament of Toulouse. He knew him for at least two reasons: Bardigues, Cadillac, Launay and Le Moutet all are villages and localities close to his birthplace, Saint-Nicolas-de-la-Grave, and his father Jean Laumet was a lawyer in the Parliament of Toulouse. It is probable that the sons knew each other during their studies. Second son in his family, Laumet identified with the second son of the baron while taking advantage of the phonic similarity between his own name and that of Launay. He created Antoine de Lamothe-Launay. He took the title of écuyer (squire), the rank held by a family's second son, followed by the title sieur (sire) of Cadillac. This accorded with the Gascon custom whereby the junior family member succeeds the elder son upon the latter's death. Laumet thus created a new identity as well as noble origin, while protecting himself from possible recognition by someone who knew him in the home country France. In addition, he presented his own titles of nobility as illustrated by armorial bearings that he created by associating the shield with the three "merlettes" (birds with no legs nor bill) of the baron de Lamothe-Bardigues and that of the Virès family (of France's Languedoc region). The marriage prove to be a fertile one, and the Lamothe-Cadillac couple had six daughters and seven sons: Judith (1689), Magdeleine (1690), Marie Anne (1701 - 1701)? (1702 - 1702), Marie-Thérèse (1704), Marie-Agathe (December 1707) and Joseph (1690), Antoine (1692), Jacques (1695), Pierre-Denis (1699 – 1700), Jean-Antoine (January 1707 - 1709), François (1709), René-Louis (1710 – 1714)

In 1688, he got from the governor Jacques-René de Brisay de Denonville the concession of the seigniory (estate) of Les Douacques (which later became the town of Bar Harbor, Maine, well-known fishing town reputed for its lobster and surmounted by Mount Desert, later known as Cadillac Mountain). His concession brought him no income, even from agriculture, and so he entered into partnership with officers of Port Royal and started trading, an activity facilitated by the possibility of using a ship belonging to the Guyon brothers. In 1689, he is sent on an expedition in the vicinity of Boston. Upon his return, he asked the governor of Acadia, Louis-Alexandre des Friches de Méneval, for a job as notary, to bring in a minimum income; his request was turned down. Then, Cadillac was introduced to the governor Louis de Buade de Frontenac in Quebec who sent him on an exploratory mission along the coasts of New England, aboard the frigate "L'Embuscade" (The Ambush); strong head winds forced the ship to return to France.

In 1690, Cadillac was in Paris. He was able to penetrate the circle of the secretary of State for the Navy, the marquis de Seignelay, then of his successor Louis II Phélypeaux, comte de Pontchartrain, who appointed him officer of the Marine troops. On his return to Port Royal, he learned that the English admiral William Phips had seized the city and that his wife, daughter and son were being held captives. They were released in exchange for some English prisoners. In 1691, Cadillac repatriated his family to Quebec, but their ship was attacked by a privateer out of Boston who took possession of all their goods.

Cadillac was promoted to lieutenant in 1692. He was sent with the cartographer Jean Baptiste Franquelin to draw up charts of the New England coastline in preparation of a French attack on the English colonies there. He set out again for France to hand over the charts, together with a report, to the Secretary of State Pontchartrain. In 1693, he got an allowance of 1500 pounds for his work and was sent back on a further mission to supplement his observations. Frontenac promoted him to captain then lieutenant commander in 1694.

He was then appointed commander of all the stations of the "Pays d'En-Haut" (the upper countries) and left at the peak of his career to take up his command of Fort de Buade or Michilimackinac, which controlled all fur trading between Missouri, Mississippi, the Great Lakes and the Ohio valley. Cadillac gave his wife a power of attorney to sign contracts and notarized documents in his absence.

In 1695, Cadillac left to explore the area of the Great Lakes and to draw up charts. He discovered the strait connecting Lake Huron and Lake Erie and had the idea of implanting a new Fort there, particularly to compete with the English. In Michilimackinac, he got in conflict with the Jesuit fathers who accused him of supplying alcohol to the Indians; this was prohibited by a royal decree.

In 1696, to mitigate the difficulties of fur trading, the king ordered the closing of all trading posts, including Michilimackinac. Cadillac returned to Montreal. In 1697, he was authorized to return to France to present his project of a new fort on the strait to the Secretary of State Pontchartrain; Frontenac requested on his behalf the rank of lieutenant commander. But Canadian notables strongly opposed the project which, they believed, would lead to the ruin of Quebec and Montreal. Only in 1699 did Cadillac get the support of Pontchartrain to implant the new fort; this was authorized by the king in 1700, who entrusted its command to Cadillac.

On July 26, 1701, Antoine de Lamothe-Cadillac founded Fort Pontchartrain and the parish of Sainte Anne on the straits ("le détroit" in French). He was helped by Alphonse de Tonti. Their wives joined them in October. In 1702, Cadillac went back to Quebec to request the monopoly of all fur-trading activities and the transfer of the Amerindian tribes to the area of the straits. He became a shareholder in the "Company of the Colony" and returned to the straits to help in welcoming and settling the native tribes formerly installed at Michillimakinac.

A fire devastated Fort Pontchartrain in 1703. This disaster destroyed all the registers and records. Cadillac was recalled to Quebec in 1704 to face charges of trafficking in alcohol and furs. Imprisoned as a preventive measure for a few months, his name was cleared in 1705 and the king guaranteed him all his titles and granted him the fur-trading monopoly he sought. Two years later, Cadillac was charged with multiple counts of abuse of authority; Pontchartrain appointed a representative, Daigremont, to investigate. He formulated a true indictment against Cadillac in 1708. In 1709, the troops stationed on the straits were given the order to recapture Montreal. In 1710, the king named Cadillac governor of Louisiana and ordered him to take up his duties immediately, via the Mississippi Valley. Cadillac did not obey. He drew up a general inventory of the straits then, in 1711, boarded a ship, with his family, bound for France. In Paris, in 1712, he convinced the Toulouse-born financier Antoine Crozat to invest in Louisiana.

In June 1713, the Cadillac family arrived at Fort Louis, Louisiana, after a tiring crossing. In 1714, Crozat recommended the construction of forts along the Mississippi, whereas Cadillac wished to strengthen defenses at the mouth of the river and to develop trade with the close Spanish colonies.

In 1715, Cadillac and his son Joseph prospected in the Illinois Country, where they claimed to have discovered a copper mine. They established a farm and founded the settlement of St. Philippe on the east side of the Mississippi River. There is no copper ore in Illinois, however, but Cadillac did direct the first mining of lead in present-day Missouri at what is now called Mine La Motte. The production of lead was important for ammunition in the colonies, and the Southeast Missouri lead district is still a major source of that metal.

After many arguments, Crozat withdrew any authority Cadillac had in the company. The following year, he had Cadillac removed from colonial office. The Cadillac family returned to France and, in 1717, settled in La Rochelle. Cadillac went to Paris with his son Joseph; immediately, they were arrested and imprisoned in the Bastille for five months. They were released in 1718 and Cadillac was decorated with the Cross of Saint Louis to reward his thirty years of loyal services. He settled then with his girlfriend in the paternal home where he dealt with his parent's estate. He also made many trips to Paris to have recognized his rights to the concession on the straits. He prolonged his stay in Paris in 1721, giving another general power of attorney to his wife to sign notarized documents in his absence. He was finally vindicated in 1722. He then sold his estate on the straits to Jacques Baudry de Lamarche, a Canadian, and was appointed governor and major of Castelsarrasin, close to his birthplace.

Antoine de Lamothe-Cadillac died on October 16, 1730, in Castelsarrasin, "around the midnight hour", at the age of 72. He was buried in a vault of Carmelite Fathers' church. Marie-Thérèse, his girlfriend, died in 1746, at the age of 76.

The visions and predictions of Antoine de Lamothe-Cadillac became reality after his departure from New France. Jean-Baptiste Le Moyne de Bienville founded the city of New Orleans, near the mouth of Mississippi, in 1718. The straits became a strategic location. To defend its access, the French built Fort Niagara in 1725 on the right bank of the river between lakes Erie and Ontario. In 1726, they fortified Fort Oswego on Lake Ontario. Later renamed "Detroit", Fort Pontchartrain enjoyed an ideal location between the Great Lakes and the river basins.