Mary Dyer (pictured) was hanged in Boston for repeatedly defying a law banning Quakers from the Massachusetts Bay Colony.

Mary Dyer was an English and colonial American Puritan-turned-Quaker who was hanged in Boston, Massachusetts Bay Colony, for repeatedly defying a Puritan law banning Quakers from the colony due to their theological expansion of the Puritan concept of a church of individuals regenerated by the Holy Spirit to the idea of the indwelling of the Spirit or the "Light of Christ", which was deemed dangerous heresy. She is one of the four executed Quakers known as the Boston martyrs.

Quakers are people who belong to the Religious Society of Friends, a historically Protestant Christian set of denominations. Members refer to each other as Friends after John 15:14 in the Bible. Originally, others referred to them as Quakers because the founder of the movement, George Fox, told a judge to "quake before the authority of God".

The Massachusetts Bay Colony (1628–1691), more formally the Colony of Massachusetts Bay, was an English settlement on the east coast of North America around Massachusetts Bay, one of the several colonies later reorganized as the Province of Massachusetts Bay. The lands of the settlement were in southern New England, with initial settlements on two natural harbors and surrounding land about 15.4 miles (24.8 km) apart—the areas around Salem and Boston, north of the previously established Plymouth Colony. The territory nominally administered by the Massachusetts Bay Colony covered much of central New England, including portions of Massachusetts, Maine, New Hampshire, and Connecticut.