The English philosopher John Locke was a vocal advocate of private property, and gave an eloquent defense of it in his "Second Treatise on Government." (More on that here.) Perhaps owing partially to that, it's sometimes been claimed that he said that this was the main reason that societies exist. It might even be claimed that he said capital punishment was an appropriate penalty for violating it through stealing - something which is vastly far from the truth, but which may seem (emphasis on "seem") to be supported by an actual quote from Locke's work - at least, when that quote is taken out of context.
Before giving the quote itself, I should foreshadow the interpretation to come a little bit, by mentioning that Locke meant something different by the word "property" than we do today (he was, after all, writing in the 17th century, whose English was very different from our own); and his broader definition of that word is stated explicitly by Locke himself in a later chapter of his book - the very work that this quote taken out of context comes from, which is the "Second Treatise on Government."
But before I give the interpretation, I will first give the quote that has been so often misinterpreted:
"Political power, then, I take to be a *right* of making laws with penalties of death, and consequently all less penalties, for the regulating and preserving of property, and of employing the force of the community, in the execution of such laws, and in the defence of the commonwealth from foreign injury; and all this only for the public good." (Source: "Second Treatise on Government," Chapter I, Section 3)
The problem with this interpretation is that the word "property" meant something different when Locke published it than it does now - it did not merely mean physical belongings. More to the point, Locke had a more specific definition in mind when he used that word, which he states explicitly in a later chapter of this book (as quoted below):
Title page from first edition of "Two Treatises of Government"
"Man being born, as has been proved, with a title to perfect freedom, and an uncontrouled 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, against the injuries and attempts of other men; but to judge of, and punish the breaches of that law in others, as he is persuaded the offence deserves, even with death itself, in crimes where the heinousness of the fact, in his opinion, requires it." (Source: "Second Treatise on Government," Chapter VII, Section 87)
Here, Locke refers to a man's "property," and defines it explicitly to be his "life, liberty, and estate" - a much broader definition than the physical belongings specified by our modern definition. A man has a "property" in his life and his liberty, according to Locke's definition; and therefore, specifying "the regulating and preserving of property" as a primary purpose of government includes the vital protections of our life and liberty - protections that no one would deny are primary to the very core functions of government, if not the core functions.
And regarding the "capital punishment" part, saying the right of making laws "with penalties of death" cannot be taken as applying specifically to breaches against one's physical belongings, as some of Locke's critics have claimed. Whether you support the death penalty or not, it is quite clear that advocating it as a punishment for murder - a breach of the right to life, which is included under Locke's definition of "property" - is a very different thing from advocating it as a punishment for stealing physical belongings, which is the narrow interpretation that Locke's critics have sometimes misattributed to him. Locke never said anything of the kind, and the criticism thus seems more the result of ignorance than an informed evaluation of his words.
If you want to know what Locke really said about private property, I have an entire blog post on the subject here; which shows how Locke's theories of private property are able to withstand criticism, with a nearly airtight argument against communism - offered long before Karl Marx was even born. (More on that at the following link.)