Francis Turretin (1623–1687) or François Turretini was a Reformed Theologian who taught in Calvin's academy in Geneva a couple generations after John Calvin had died. He is most famous for his timeless and massive systematic theology titled: "Institutes of Elentic Theology" ("IET" henceforth). ("Elentic" basically synonymous with "apologetics.") I recently finished reading a new translation of Turretin's work by George Musgrave Giger and edited by James T. Dennison. This recent translation weights in at 2,311 pages, divided into three volumes and costs almost $85 for the best price on amazon.
I began reading this Systematic Theology (ST from now on) after reading Michael Horton's recent and awesome systematic theology that I read earlier this year titled: "The Christian Faith." Horton had engaged with Turretin many times through his ST. The beauty of Turretin's IET is that it is the eminent ST that held the field between Calvin's institutes in the 16th century until Charles Hodge's ST in the 19th century. The book has an anecdote about how Turretin's latin original was in the library for students at Princeton to look up the footenotes in Hodge's ST.
Overall, Turretin's IET is a conservative exposition of the Reformed Faith that is trending towards the Protestant Scholasticism of his time. Most arguments are stated against a specific opponent who represents that belief where Turretin either "affirms", "denies", or clarifies the truth doctrine. In many ways Faustus Socinus was to Turretin as Michael Servetus was to John Calvin. Socinus was a 17th century anti-trinitarian that appears regularly in the IET.
Turretin primarily engages Robert Bellarmine, who is a Doctor of the Catholic Church (1542 – 1621), who's Counter-Reformation works are the primary target of Turretin's ST (in terms of "elentic"). To Turretin, Bellarmine represents Roman Catholic dogma in the 17th century.
Overall, its an amazing ST by Turretin, and the most fascinating aspect of IET is that it's format and program of contents established the framework by which all other ST's to come would organize their material. If you've read any ST, then you've read Turretin.