Stanley is the main character of Holes, and he ends up being the awkward and unlikely hero of the book. He does not have any friends from school and is often picked on by his classmates and the school bully. Stanley's family is cursed with bad luck and although they do not have much money they always try to remain hopeful and look on the bright side of things. Stanley shares these traits with his family and despite him not having a lot of self-confidence, he is not easily depressed. This helps him adjust to the horrendous conditions of Camp Green Lake. As the book progresses, Stanley slowly develops physical strength and personal strength. Stanley is displayed as fat and overweight in the beginning but by the end, he has toughened up and become a fit and healthy kid.

Hector Zeroni or Zero is a kid who has been homeless for most of his life, and his mother abandoned him when he was young. Zero has not had much of an education so he does not know how to read or write. Despite all the bullying that he has faced, Zero knows that he is smart and he has a sense of standing up for himself. At first, he is presented as a strange character because he rarely speaks and always walks around with a straight face. Eventually, when Zero becomes friends with Stanley, it is revealed that Zero is silent because he does not like answering questions and does not like how people always mock him. Zero suffers so much pain in his life that he eventually cannot stand Camp Green Lake anymore and he runs away, finding his way back after wanting to uncover the true treasure of Camp Green Lake. 

Mr. Sir is the mean counselor who is responsible for telling the rules and expectations at Camp Green Lake to new campers like Stanley. Mr. Sir only uses a gun to protect himself and others at the camp from dangerous animals like rattlesnakes and yellow-spotted lizards. Mr. Sir in a way takes pleasure in scaring the campers. 

Mr. Pendanski is in charge of tent D (Stanley's tent). He seems to be friendly but is proven to be as mean as the Warden and Mr. Sir. This is shown by his constant taunting of Zero and by his lack of concern for the safety of Stanley and Zero when they run away.

The Warden is the cruel leader of Camp Green Lake, as well as the owner of the land where the camp is situated. While Mr. Sir is characterized by his strict approach and Mr. Pendanski by his polite meanness, The Warden has an icy, polite attitude. However, her outer calm hides her  and greedy disposition. 

Tent D is the tent that Stanley is assigned to for his one-and-a-half-year stay at Camp Green Lake. Tent D consists of  X-ray, Stanley, Zero, Armpit, Squid, Zig-Zag, Magnet, twitch, and Barf Bag.  X-ray is displayed as the leader of the group as he has been there the longest and is first for everything, however he is one of the smallest in the group.