Final answer:
Thomas Jefferson first articulated the idea of unalienable rights in the Declaration of Independence.
Step-by-step explanation:
The Founding Father who first articulated the idea of unalienable rights in a founding document of the United States was Thomas Jefferson. In the Declaration of Independence, Jefferson wrote that all men are created equal and endowed by their Creator with certain unalienable rights, including life, liberty, and the pursuit of happiness.