John Locke.
One of the key phrases in the Declaration “life, liberty, and the pursuit of happiness” was from Locke’s Two Treatises of Government. Locke developed the idea that all mankind is created equally and that our fundamental human rights (for life, liberty, and the pursuit of happiness) should never be taken by the government.
The original writers of the Declaration of Independence, namely Jefferson, took inspiration and included some of Locke’s ideas.