Victor is a fifteen-year-old from the small Mexican farming village of Los Árboles. After his father dies in a construction accident in the United States, Victor assumes the role of provider for his mother and younger siblings. Nicknamed "Turtle" for his cautious, deliberate nature, he works the family corn fields until plummeting crop prices force him to plan a dangerous, unfunded trip across the border. He draws mental fortitude from his father's stories about the jaguar.

Rico is Victor's childhood best friend. He possesses a bold attitude and a deep fascination with American culture. He wears his bleached hair short under a yellow baseball cap and dreams of owning a car and shaking hands with Mickey Mouse. Supplied with coyote money from his older brother in Tucson, he sneaks away from his village. This action abandons his parents' expectation that he will attend trade school and care for them in their old age.

Miguel is an older, experienced border crosser whom Victor spots on a bus to Nogales. He travels independently after a coyote abandoned him on a previous trip. Pragmatic and carefully prepared, he maps out his own routes through the mountains to avoid capture. He seeks work in El Norte to provide for his wife and four children, dispensing practical advice that reminds Victor of his own father.

Tony Jarra, The Mosquito, is a wealthy former gang member operating near the border town of Sasabe. He works as a pollero and drug smuggler, sporting gold chains, diamond studs, and a large chest tattoo of El Cristo Rey. He keeps a gun in his vehicle and recruits vulnerable travelers to carry supplies for his smuggling operations across the desert.

Julio is a teenager from Honduras who rides freight trains toward the Arizona border. Having previously worked at a turkey farm in Texas before being deported, he understands the routines of the long journey. He shares his knowledge of train-hopping with Victor and plans to enter the United States by floating through storm runoff tunnels.

Dave is a friendly motorist whom Victor and Rico encounter on a mountain road. He studies the rare jaguars that populate the high terrain near the border. His interest in the local wildlife makes him receptive to the boys' story, leading him to offer them transportation to Tucson.

Reynaldo is Rico's oldest brother, currently living in Tucson, Arizona. He works cleaning swimming pools and selling cars, supplying Rico with the cash needed to hire a border guide.

Senor Rivera is a farmer in Los Árboles and Rico's father. He explains the devastating effects of free trade agreements on local agriculture to Victor. He expects his youngest son to stay in Mexico and provide care during his old age.

Victor's mother manages the household in Los Árboles. When Victor decides he must travel north, she entrusts his safety to Our Lady of Guadalupe and gives him her blessing before he departs.

Victor's late father died four years before the story begins, killed by a collapsing wall while building a high school in South Carolina. He passed down stories of his ancestors and the powerful tigre.