Americans are confused about Thanksgiving. The Pilgrims whose Plymouth feast generates the story are remembered as pioneers of freedom of conscience, brave souls who crossed an ocean for the sake of religious liberty.

Not quite.

The November feast, with turkeys and cranberries, is a creation myth, starring Miles Standish, William Bradford, and the Wampanoag chief, Massasoit. But the figure who most powerfully created American consciousness, coming a little later, was one who risked everything to rebel against what was begun in Plymouth. What we celebrate on Thanksgiving isn't the theocracy of Massachusetts, but the ideas of Roger Williams, a Puritan who defended the right, one could say, to be religiously impure.

A magnificent new biography of Williams was published this year. In "Roger Williams and the Creation of the American Soul: Church, State, and the Birth of Liberty," author John M. Barry shows that the American soul's true birthplace is "the Rhode Island and Providence Plantations," which Williams founded after Massachusetts banished him, and for which he obtained a royal charter 350 years ago next year.

A Cambridge-educated minister and former tutor to John Milton, Williams arrived in Massachusetts from England in 1631, eleven years after the Mayflower landed in Plymouth. He was quick to reject the legal basis of the Bay Colony because the settlers did not recognize Indian claims to the land they took. Like most Puritans, he deplored the beliefs and practices of eccentric cults like the Quakers. Yet, unlike church elders who eventually saw to the hanging of Quaker Mary Dyer on Boston Common, he believed that such nonconformists should worship as they chose. "Soul liberty" was his watchword.

Indeed, Williams insisted that because the magistrate's duty is to protect the "permission of conscience" of each citizen, the magistrate must be religiously neutral. It was Williams, writing more than a century before Jefferson, who first used the phrase "wall of separation" to define the relationship between church and state.

For such "diverse, new, and dangerous opinions," Williams was forcibly exiled into the wilderness from Massachusetts in 1636. Alone, and at risk, Williams was offered refuge, in territory still under Wampanoag control to the south, by none other than Massasoit. The Plantation at Providence, established by Williams at the head of Narragansett Bay, would be very different from Massachusetts - beginning with the compensation paid to the Wampanoag for the land, and with Williams's resolute refusal to betray the Indians who had befriended him.

The experience of banishment only reinforced Williams in his expansive outlook. He saw that the rights he claimed for himself belonged to all, including Africans (The Rhode Island General Assembly outlawed slavery in 1652) and women (Anne Hutchinson, another dissenter expelled from Massachusetts, joined him in the application for the Rhode Island charter).

He was regarded as a forerunner of John Locke, whose landmark "On Toleration" was published in 1689, six years after Williams's death. But in fact, the founder of Providence upheld a tolerance of which Locke, who justified the exclusion of Catholics and atheists, fell short. Williams wrote, "I commend that man, whether Jew, or Turk, or Papist, or whoever, that steers no otherwise than his conscience dares."

Williams believed, in effect, that even the intolerant must be tolerated, which would become a bedrock principle of liberal democracy.

As time has passed, the concept of religious freedom itself has been a source of confusion; consider the Catholic bishops' failed attempt to influence recent U.S. elections with what they called a "religious liberty campaign." The bishops, in alliance with other conservative Christians, made issues not only of reproductive rights, but of gay marriage, contraception, and even Obamacare. These faith intrusions into politics suggested that the actual meaning of "religious liberty" remains contested.

At Thanksgiving, it is right to look back gratefully at those who created the American ideal. In criticizing the original theocracy, and then in constructing a practical alternative enshrining what would be called "liberty and justice for all," Roger Williams did indeed create the American soul. He's the founder to whom, therefore, the nation's deepest thanks are due. But the way to express such gratitude is by protecting authentic religious liberty from those who, using the phrase as a banner, would destroy it.