Question

Which Enlightenment thinker believed that it is a government's job to protect the natural rights of life, liberty, and property?

Answer 1

John Locke
he wrote a book called Two Treatises of Government
Here he explained that all men have natural rights: life, liberty, and property
The people and the government have this "contract" where the government's purpose is to protect those rights while the people respect the government.  If the people feel the government is not doing their job, they have the right to rebel.

Answer 2

I know this! It's John Locke