Final answer:
John Locke argued that all people are born free in a state of nature and endorsed the formation of governments by the consent of the governed. He believed in natural rights and the concept of popular sovereignty.
Step-by-step explanation:
The philosopher who argued that all people are born free in a state of nature, and that the government should exist only with the consent of the governed is John Locke. He was an advocate for the concept of popular sovereignty and believed in natural rights such as life, liberty, and property. Locke's views were elucidated in his work, the Second Treatise of Government, where he described a state of nature where individuals, by their own consent, form a government to protect their natural rights and enforce moral laws, known as natural law. This contrasts with Thomas Hobbes, who believed in a more authoritarian government necessary to manage the state of nature he described as a war of 'every man against every man.'