To respond to ModernAngel's assertion and "proof" that Robert Heinlein is not a philosopher, I would point out that by his logic, Plato would not qualify as a philosopher either. As an aside, I am no heinleinphile and have not read the man's books.
Plato's "philosophy" was expressed through his characters. In general he used Socrates and a few of his contemporaries, but make no mistake; these were literary characters in fictional retellings of dialogues, few of which actually occurred. Plato didn't just have characters speak what was on his mind; he used them to develop opposing and alternate viewpoints, as in The Symposium. He even went so far as to tell compellingly realistic, yet fictional fables in order to make his point, as with the story of Atlantis.
A common theme in Plato's work was homosexual activity. I do not know whether Plato practiced the kinds of things mentioned in The Symposium and The Republic, but that is irrelevant. Regardless of the significance of classical man-boy love affairs in Greek society at large, or our judgment of these relationships as immoral, they remain a significant part of the settings of his books, and he uses them to make important points. "Perversion" does not make a philosophy necessarily bad.
Plato was not what we would call a "professional academic." He made some money off of his writings, but that makes him more of an author than an academician. Plato had a single teacher of whom we have any significant knowledge, Socrates. In his time, there was no such thing as "peer review" nor do I believe it has ever been common practice for philosophers to submit their writings for such review; that sort of process is more a part of empirical science than philosophy. Prior to Plato, there were no real opposing viewpoints, and even his greatest student, Aristotle, differed in perspective only slightly from the master.
Does all this mean Plato was not a philosopher? No. I do call that philosophy, because philosophy is not thinking according to some arbitrary set of rules and guidelines, but, as Socrates encouraged, the pursuit of our passion for wisdom and knowledge of ourselves. Anyone who seeks such wisdom is, by definition, a philosopher.