Final answer:
John Locke had the greatest influence on Thomas Jefferson's ideas in the Declaration of Independence, providing the philosophical basis for the principles of natural rights and government by consent.
Step-by-step explanation:
The individual who had the biggest impact on Thomas Jefferson's ideas reflected in the Declaration of Independence was John Locke. Locke, an English philosopher, wrote influential works, including the Second Treatise of Government, which espoused principles of individual rights and government by the consent of the governed. These concepts were central to the Declaration, particularly the ideas of unalienable rights such as life, liberty, and the pursuit of happiness. In essence, Locke's theories provided a foundation for Jefferson's rationale in drafting this seminal American document.
For instance, Locke's philosophy argued that all men are endowed with certain natural rights and that governments are instituted to protect these rights. This concept of individual rights significantly influenced Jefferson, evident in the Declaration's assertion that humans possess inalienable rights, which governments should protect, not violate.