Robert Filmer was a Kentish gentleman and royalist who wrote in the 1630s and 40s and published little in his lifetime. Patriarcha appeared in 1680, twenty-seven years after his death, when the exclusion crisis made it useful; it is remembered because the two most important works of English political theory in the following decade were written to refute it.
His argument begins by denying the premise every rival theory assumed. Men are not born free and equal. Everyone is born subject — to a father — and paternal authority is not contractual, consented to, or revocable. God gave Adam dominion over Eve and over the earth, that dominion descended by generation to the patriarchs and thence to kings, who are fathers of their peoples and hold their authority by the same title. Kingship is therefore natural, not instituted; it is prior to and the source of the family's law rather than a construction of free men; and there never was a state of nature in which anyone was at liberty to consent to anything.
The negative half is more effective than the positive. Filmer presses hard on the difficulties of consent theory and asks questions his opponents had evaded: when did this original contract occur, who were the parties, why should the agreement of ancestors bind descendants, why should a majority bind a dissenting minority, and how could a scattered multitude ever have assembled to make it. He observes that if the whole world's people must consent, no legitimate government has ever existed. Locke and Sidney both found these questions harder than they admitted.
He named his real targets precisely: the Jesuits Bellarmine and Suárez, who had argued that political power comes from God to the community and reaches the ruler by consent, and the Calvinist resistance theorists who said the same in another idiom. Filmer saw that popery and puritanism had converged on a single doctrine, and set out to deny its foundation.
Sidney answered with the Discourses Concerning Government and was executed with the manuscript used as evidence against him. Locke answered with the First Treatise, an exhaustive demolition of the scriptural genealogy, before building his own case in the Second. Filmer lost the argument so completely that the First Treatise is now rarely read — which obscures how seriously he had to be taken.