The first systematic theory of natural rights was developed by John Locke. In the 17th century, Locke articulated the idea that individuals possess inherent rights, such as life, liberty, and property, which governments must respect. His writings laid the foundation for modern democratic thought and influenced subsequent political philosophers. Locke's theories can be traced in the U.S. Declaration of Independence, particularly in the assertion of unalienable rights, highlighting the importance of individual freedoms within societal structures.