Many people would argue that Thomas Jefferson himself was an Enlightenment philosopher, but if we are looking for someone besides Jefferson, the answer would be John Locke. While Locke was active as a writer before the eighteenth century Enlightenment, his works were very influential among the thinkers and writers generally associated with the Enlightenment. Jefferson famously asserted that Locke was, along with Francis Bacon and Isaac Newton, one of the three greatest men who ever lived. Locke's influence can be found in the first section of the Declaration. Here Jefferson and the members of the Continental Congress assert that "all men are created equal" and that they are "endowed by their Creator with certain unalienable rights," including "life, liberty, and the pursuit of happiness." In his Second Treatise on Civil Government Locke had asserted the following:
Man being born, as has been proved, with a title to perfect freedom, and an uncontrolled enjoyment of all the rights and privileges of the law of nature, equally with any other man, or number of men in the world, hath by nature a power, not only to preserve his property, that is, his life, liberty and estate...
The similarities should be obvious. Locke and Jefferson both argued that man was born free and equal to all other men, and that each man had a natural right to life, liberty, and property. The Declaration goes on to say that the purpose of government was to "secure," or protect, these rights, and that if a government instead takes those rights away, men had a right to replace the government with another. This too was a Lockean idea, derived from this passage (among others) from the Second Treatise:
but in such cases...[that the people] are persuaded in their consciences, that their laws, and with them their estates, liberties, and lives are in danger, and perhaps their religion too; how they will be hindered from resisting illegal force, used against them, I cannot tell.