I assume that the idea of property already existed in ancient Greece, else there would be no slaves -- at least no privately owned slaves. Yes, I know that litte about the Greeks.
Who was the first philosopher of individual property -- as in ownership? If that's the same as asking who was the first philosopher of the state, then I may delete the question.
I read about the right to property on wikipedia
The Levellers emerged as a political movement in mid-17th century England in the aftermath of the Protestant Reformation. They believed that property which had been earned as the fruit of one's labour was sacred under the Bible's commandment "thou shall not steal". As such, they believed that the right to acquire property from one's work was sacred. Levellers' views on the right to property and the right not to be deprived of property as a civil and political right were developed by the pamphleteer Richard Overton. In "An Arrow against all Tyrants" (1646), Overton argued:
To every individual in nature is given an individual property by nature not to be invaded or usurped by any. For everyone, as he is
himself, so he has a self propertiety, else he could not be himself; and of this no second may presume to deprive of without manifest violation and affront to the very principles of nature of the rules of equity and justice between man and man. Mine and thine cannot be, except this. No man has power over my rights and liberties, and I over no man.
But it begins with the renaissance, and surely the right to individual property was exercised long before that?