Cornelius Nepos, a Roman historian from early antiquity, wrote fondly of an Athenian general named Thrasybulus: “If excellence were to be weighed by itself, apart from luck, I believe I would rank this man first of all. This much is certain, I put no one ahead of him in sense of honor, steadfastness, greatness of soul and love of country.”

Despite repeatedly rising to save Athenian democracy from the clutches of oligarchy, Thrasybulus, unlike some of his more outspoken and demagogic contemporaries, has largely been lost to the annals of history. Nevertheless, with high and fitting praise, his memory has been kept alive by Professor Donald Kagan, who has placed the overlooked general in a prominent position within his renowned course, “Introduction to Ancient Greek History.”

After forty-four years at this University, though, Professor Kagan is set to retire, giving his last classes to undergraduates this week. And while Thrasybulus may be losing his finest champion, we are losing our Thrasybulus.

To Yale, Professor Kagan has given an almost indescribable tenure — one defined as much by his character as his mind. Much like Thrasybulus, Professor Kagan’s defining contributions came not from great moments of stability or from the comfortable place of the majority, but rather from hard moments in the service of principle. As the Spartans bore down on the Athenian democracy, so did numerous academics on the Liberal Arts.

His career embodies not just a defense of the art of history, but more importantly, the heart of the academy.

Looking first at his contributions to the study of history, it is implausible for any thoughtful observer to place Kagan anywhere but in a class of his own. Simply put, he very well may be the greatest modern historian of the Ancient Greek world. Speaking of the National Humanities Medal recipient’s work, the New Yorker wrote: “The temptation to acclaim Kagan’s four volumes [on the Peloponnesian War] as the foremost work of history produced in North America in this century is vivid.”

When a relatively new professor, Kagan was one of the few to hold class during the savagely intimidating Vietnam protests. In positions of leadership, from Chairman of the Classics Department to the head of Directed Studies, Kagan stood up for meritocratic hiring processes and guided, structured curricula, in spite of the surrounding consensus to the contrary. Even in some of his defeats, from championing the attempted Bass-sponsored program on Western Civilization to the state of free speech at Yale, Kagan’s bravery often spoke larger than the causes themselves.

This summary, though, is overwhelmingly insufficient — and not simply because of its concision. It is missing an intangible quality that every student of Professor Kagan’s seminars knows incredibly well; a quality that you could hear about from a student of ’82 as much as ’12.

Professor Kagan’s history seminars are unlike many at Yale. He reveres intellectual debate, but is unflinching in the assertion that there are such things as right answers and necessarily important facts.

Yet, amazingly, the most striking quality of his class is the deep-rooted humility that a mind of his stature exhibits. He is quick to make a self-deprecating joke (“Don’t trust a word that guy says,” when a student quotes one of his books back to him) or to jab at the lofty latitude academia often allows itself (“That’s over my head. You sound too much like a professor.”).

In the end, his intellectual ferocity is balanced by a profound kindness, compassion and care for his students. After so long here, it’s difficult to think he hasn’t heard every answer before. But you’d never know it. Even as the most prominent man of his field, he can make any undergraduate feel like he is hanging on their every word. At the end of the term, while a student can be overpowered by the amount he has learned, he is all the more affected by the amount he has grown; forged in the loving cerebral crucible that is Donald Kagan’s classroom.

At the end of this term, Yale is saying farewell not only to one of its greatest minds, but greatest souls; someone who not simply added to the laurels of this University, but personified its spirit. He has been our Thrasybulus, someone with no superior in sense of “honor, steadfastness, greatness of soul and love (of God), of country (and of Yale).”

Harry Graver is a junior in Davenport College. Contact him at harry.graver@yale.edu .