Matteo (Matt) Alacrán: The protagonist, Matt is the most recent clone of El Patrón. Raised in close proximity to the Alacrán estate, Matt is constantly reminded of his position as a clone, being of equal status to cattle. As such, Matt grows up wanting to prove himself better than anyone else, so they will be forced to acknowledge him. The House of the Scorpion follows Matt's journey from a young boy growing up in a small house with his caretaker, Celia, to his subsequent realization of his autonomy and self-worth. Throughout much of the book, Matt struggles to find balance between his selfishness and desire to prove himself, with being kind and moral to others. At first, Matt views El Patrón as a very dear man whom he cares about deeply, yet slowly starts to realize the cruel nature of the man. Helped along the way with family and friends, Matt realizes the corrupt nature of Opium and eventually seeks to change the drug-powered land for the better.
Matteo (El Patrón) Alacrán: A powerful drug-lord in the land of Opium. El Patrón extends his life by replacing his body parts with those of younger clones. By doing so, he has lived far longer than the average person at 140 years old. He likes to give his clones what he considers a luxurious life, because he lives vicariously through his clones experiencing a life of privilege he never had growing up. When Matt expresses musical talent, he immediately hires a music teacher so he can enjoy the talent he never got to foster. Though he is affectionate to Matt, he is cruel and domineering towards everyone else, including his own family. He is quick to turn people into eejits, the mindless slaves that work his fields and tend to other manual work. He is widely feared for his cruelty and power. Everything, from the land, wealth, power, and people, belongs to him and him alone. When he has a heart attack due to Matt's failure to provide a heart, he poisons his entire family to ensure his empire and all his possessions fall with him.
Celia: Matt's caretaker and mother figure, Celia is a kind, caring woman who protects Matt fiercely from any threat. She goes so far to protect him that when she finds out Matt's heart is due to replace El Patrón's, she begins to poison Matt with tiny amounts of arsenic. Not enough to kill Matt, but certainly kill someone with a weaker system. Described as a hardworking woman, Celia always made sure to make time for Matt, carrying him to bed every night, even past the point of exhaustion where she almost collapsed after working all day. Matt grows up in her care learning love despite being treated negatively by others, describing her snores to be a comforting, familiar sound.
Tam Lin: Both Matt and El Patrón's body guard, he is described as having curly brown hair, blue eyes, and covered in scars. He has a tough, unfriendly exterior, though he proves on multiple occasions he cares for Matt, such as when he saves him from choking while he is young and later, helping Matt escape into the mountains to avoid a fate of dying as a clone. Tam Lin spends a lot of time at Celia's house with Matt, teaching him survival skills such as cooking and camping. Before working for El Patrón, Tam Lin was a Scottish nationalist, described by others as a terrorist for attempting to blow up a government official. Instead, he accidentally killed 20 children. Deciding to make amends for the wrongs he committed at the end, Tam Lin allows El Patrón to poison and kill him along with the rest of the Alacrán family.
