Hamm controls everyone in the play while having absolutely no control over himself or his environment. He bosses Clov around to no end and silences his parents, Nagg and Nell, whenever they talk for too long, but as for his own unrelenting misery and the gray, unchanging fallout around him, he is powerless. He is like the King in chess, the most powerful piece whom all others serve, but who is also the most vulnerable.
Hamm's great fear is that existence is cyclical; that beginnings and endings are fused in the grand scheme of things and that life will spring up again. But contradictions confuse his desires. He is terrified of the flea and rat that Clov finds and wants to exterminate them in case "humanity might start from there all over again," but he also proposes that he and Clov go South to other "mammals." He wants to be left alone, but clings to Clov and does anything he can to pull him back into the room. Most confusingly, he believes that nature is changing, though all evidence indicates that it has "zero" change. Under his misanthropic exterior is a desperate neediness, a fear of being alone that has been with him ever since childhood (as Nagg tells it).
Light, which is used as a symbol of hope and life, expresses many of the nuances of Hamm's personality. He is attracted to whatever light there is in the gray world, asking Clov to push him under the window so he can feel it on his face. But we also learn that he withheld light from someone named Mother Pegg, who died of darkness. Compounding this is Hamm's blindness; he has been cursed with darkness, and he wants others to share the same miserable fate. When he polishes his dark glasses, it is a futile routine of equal parts poignancy and resentment.
Indeed, Hamm's routines are all futile. As in many of Beckett's plays, routines are what humans perform to convince themselves that death is not imminent, that each day is the same. Ironically, the empty, absurd practices only inch them closer to death. In the "endgame" of his life, Hamm is only partially reconciled to death—he wants it to come, but he admits that he "hesitate[s]" to "finish." The routines fill this middle ground, staving off death while drawing it ever closer. Hamm is attached to the middles of things, harboring a compulsive need to return to the middle of the room. Much of his routine day is spent bickering with Clov, whom he took in as a child years ago and to whom he became a surrogate father. Both men question why they put up with each other, and at one point Hamm suggests that Clov help him out of compassion. The real reason is that both are dependent on each other and afraid to leave and be alone, despite their constant threats (Beckett has compared their relationship to his own with his wife in the 1950s, when both were afraid to leave each other though they wanted to). The play takes a surprisingly moving turn at the end when both men sincerely thank each other for their services before Clov's departure, but after Clov has returned, unbeknownst to Hamm, we get the feeling that they will be back at square one tomorrow.
Clov is the submissive Knight to Hamm's King; he staggers around erratically, performing errands and letting Hamm virtually ride him (Hamm pushes him around on his chair). Nevertheless, he stands up for himself at times, even going so far as to hit Hamm with his toy dog. He is less hostile than Hamm, but he harbors a deeper sadness. While Hamm never had anything, it seems, Clov seems to have lost something dear to him; the story Hamm tells about the beggar and his child may be a reference to Clov's father and Clov (Beckett was ambiguous about this in conversation). No matter what the situation, it is irrefutable that at some point Hamm took Clov in and became a father figure to him. While Clov wonders repeatedly why he stays with Hamm, his lifelong sense of obligation is one apparent reason out of a possible three. He shares another major reason with Hamm; both men are afraid to be alone, despite their constant declarations otherwise. The final reason, which Hamm offers at the end, is that Clov has compassion. Though Clov shatters the illusion that mercy is one of life's consolations in his final monologue, it may indeed be that from the wasteland of their post-apocalyptic endgame he has retained some humanity.
Clov's other main similarity to Hamm is his fear that existence is cyclical; he kills (or tries to kill) the flea and rat, potential regenerators, and he wants to kill the boy at the end, the "potential procreator." He opens the play by announcing, "it's finished," and brings up a question that underscores the play's ideas of repetition: when does an accumulation of distinct grains become a heap? In Clov's view, since each grain is always a distinct grain, then what we call a heap is really an "impossible heap," since it is made up of those distinct grains. In the same vein, a life is not really a life, but a sequence of moments—until, of course, death closes off those moments and the moments can be viewed as a single unit. For Clov, these moments are simply repetitive, part of a repetitive existence, and finality is impossible—he laughs at Hamm's suggestion that they are beginning to make meaning in their world since a repetitive, cyclical world is in a constant state of flux and conclusion is unattainable. This lack of finality and the fusion of beginnings and endings is the ultimate reason for his inability to leave Hamm at the end of the play: he cannot leave, for leaving would imply that there is such a thing as ending one's tenure in one place and beginning a new one elsewhere.