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.