She may not be famous in the current celebrity sense, but Mary Dyer was a rock star in the religious freedom world. Her "sin" was converting from Puritanism to Quakerism, because Quakers believed that people could hear directly from God, without needing an intermediary like a clergyman. This was a really big deal in the 1600s, as it threatened the authority of the church leaders, who governed the colony, and banned Quakers from living in Massachusetts [sources: PBS, Robinson].
Dyer went into exile in Rhode Island. However, she returned to Boston to support two friends who were imprisoned for their Quaker beliefs. All three were sentenced to death but reprieved and banished. But Dyer came back again, determined to speak out for religious freedom. She was hanged in Boston Common and buried in an unmarked plot in 1660. (Some say her body was taken to the family farm). Remorse over this unnecessary execution led to a lessening of anti-Quaker laws and eventually to the Rhode Island Royal Charter of 1663, legally granting freedom of religion. Today, a statue of Mary Dyer stands in Boston Common, where her life famously ended [sources: National Women's History Museum, Robinson].