The central character of Willie Stark (often simply referred to as "the Boss") undergoes a radical transformation from an idealistic lawyer and weak gubernatorial candidate into a charismatic and extraordinarily powerful governor. In achieving this office Stark comes to embrace various forms of corruption and builds an enormous political machine based on patronage and intimidation. His approach to politics earns him many enemies in the state legislature, but does not detract from his popular appeal among many of his constituents, who respond with enthusiasm to his fiery populist manner.
Stark's character is often thought to be inspired by the life of Huey P. Long, former governor of Louisiana and that state's U.S. senator in the mid-1930s. Huey Long was at the zenith of his career when he was assassinated in 1935; just a year earlier, Robert Penn Warren had begun teaching at Louisiana State University. Stark, like Long, is shot to death in the state capitol building by a physician. The title of the book possibly came from Long's motto, "Every Man a King."
In his introduction to the Modern Library edition, Warren denied that the book should be read as either praise for Huey Long or praise for his assassination. However, Warren did not deny that Long served as an influence or inspiration for Stark:
One of the unfortunate characteristics of our time is that the reception of a novel may depend on its journalistic relevance. It is a little graceless of me to call this characteristic unfortunate, and to quarrel with it, for certainly the journalistic relevance of All the King's Men had a good deal to do with what interest it evoked. My politician hero, whose name, in the end, was Willie Stark, was quickly equated with the late [US] Senator Huey P. Long....
This equation led, in different quarters, to quite contradictory interpretations of the novel. On one hand, there were those who took the thing to be a not-so-covert biography of, and apologia for, Senator Long, and the author to be not less than a base minion of the great man. There is really nothing to reply to this innocent boneheadedness or gospel-bit hysteria. As Louis Armstrong is reported to have said, there's some folks that, if they don't know, you can't tell 'em... But on the other hand, there were those who took the thing to be a rousing declaration of democratic principles and a tract for the assassination of dictators. This view, though somewhat more congenial to my personal political views, was almost as wide of the mark. For better or worse, Willie Stark was not Huey Long. Willie [Stark] was only himself....[T]he difference between the person Huey P. Long and the fiction Willie Stark, may be indicated by the fact that in the verse play [Proud Flesh] the name of the politician was Talos — the name of the brutal, blank-eyed 'iron groom' of Spenser's Fairie Queene, the pitiless servant of the knight of justice. My conception grew wider, but that element always remained, and Willie Stark remained, in one way, Willie Talos. In other words, Talos is the kind of doom that democracy may invite upon itself. The book, however, was never intended to be a book about politics. Politics merely provided the framework story in which the deeper concerns, whatever their final significance, might work themselves out.
Jack Burden is the novel's narrator, a former student of history, newspaper columnist, and personal aide to Governor Willie Stark.
His narrative is propelled in part by a fascination with the mystery of Stark's larger-than-life character, and equally by his struggle to discover some underlying principle to make sense of all that has happened.
In narrating the story, Jack commingles his own personal story with the political story of Governor Stark. His telling of these two stories side by side creates a striking contrast between the personal and the impersonal. While his wry, detached, often humorous tone suggests an attempt to stand apart from the other characters' passions and intrigues, the highly personal content of his narrative suggests an awareness that he cannot truthfully remove himself and his own history from the story of Willie Stark, because his own story has paralleled and helped shape the tragic outcome of Stark's story.
Jack's overall character development might be roughly described as a journey away from an amoral perspective on human history as a chain of uncontrollable events, toward a belief in the fundamental interconnectedness of all of history. In other words, he might be said to trace a path from refusal to acceptance of personal responsibility. On the other hand, one defining trait that remains a constant throughout Jack's development is a passion for discovering the truth of history.
"And all times are one time, and all those dead in the past never lived before our definition gives them life, and out of the shadow their eyes implore us. That is what all of us historical researchers believe. And we love truth." [p. 342]
Anne is Jack Burden's childhood sweetheart and the daughter of Willie Stark's political predecessor, Governor Stanton. Many of the novel's passages recounting Jack's life story revolve around memories of his relationship with Anne. Like many of Jack's friends, Anne disapproves of Willie Stark. However, in the wake of a devastating revelation regarding one of her father's moral lapses, she has an affair with Stark.
Adam is a highly successful doctor, Anne Stanton's brother, and Jack Burden's childhood friend. Jack comes to view Adam Stanton as the polar opposite of Governor Stark, calling Adam "the man of idea" and Stark "the man of fact". Elsewhere, he describes Adam's central motivation as a deep need to "do good". Governor Stark invites Adam to be director of his pet project, a new hospital and medical center. The position initially strikes Adam as repugnant because of his revulsion to Stark's politics, but Jack and Anne ultimately persuade him to accept the invitation, essentially by removing his moral high ground. Adam's sense of violation as a result of his entanglement with Governor Stark proves violently tragic when he is informed by Lieutenant Governor Tiny Duffy that Stark has been sleeping with his sister. His pride demolished, Adam finds the Governor at the Capitol building and shoots him. To the extent that Willie Stark's story may have been loosely based on real-life events, the inspiration behind Adam Stanton's character would have been Dr. Carl Weiss.
Judge Irwin is an elderly gentleman whom Jack has known since childhood, a man who is essentially a father-figure to him. Willie Stark assigns Jack the task of digging through Irwin's past to find something from the past with which Irwin can be blackmailed. Jack investigates thoroughly and finds what he is looking for: an incident many years ago when Judge Irwin took a bribe to dismiss a lawsuit against a fuel company, resulting in the personal destruction of a man named Mortimer Littlepaugh. Jack presents the incriminating evidence to Irwin, and before he has a chance to use it against him, Irwin commits suicide. Only at this point does Jack learn from his mother that Irwin was his father.
One of Jack Burden's first major historical research projects revolves around the life of a 19th-century collateral ancestor, Cass Mastern, a man of high moral standards and a student at Transylvania College in Kentucky (Robert Penn Warren's native state). Cass's story, as revealed through his journals and letters, is essentially about a single betrayal of a friend that seems to ripple endlessly outward with negative consequences for many people. In studying this fragment of Civil War–era history, Jack begins to suspect (but cannot yet bring himself to accept) the idea that every event has unforeseen and unknowable implications, and that all actions and all persons are connected to other actions and other persons. Jack suggests that one reason he is unable to complete his dissertation on Cass's life is that perhaps "he was afraid to understand for what might be understood there was a reproach to him."
Cass Mastern and his moral challenges parallel those of Jack, something Jack does not understand when he is doing his doctoral dissertation on Mastern and one of the reasons that Burden abandons it. It is only at the end of the novel that Jack realizes this.