Ruiz (birth name: José Antonio Torresola Ruiz [note 1]) was born in Paterson, New Jersey to Frank Torresola and Hilda Ruiz, a Puerto Rican couple who had moved to the city. After being born, he was initially adopted by his grandmother, Concepción, as his mother was 15 years old. Afterwards his custody passed to his parents and he was raised at Union City, along his brothers Viti and Junito. He received his primary and secondary school education in Paterson, where his father served as education commissioner.
At the age of 5, Ruiz played percussion instruments at the Roberto Clemente Park in Trenton and at other city venues. One of these performances earned him an award at a show held at the Majestic Theater in Paterson. During the following years, he continued performing with the support of his parents, meeting artists like Tito Puente in the process. Despite this, Ruiz was not enrolled in formal singing classes and mostly depended on practice. During this time, he developed a friendship with Joe Salvador, through which he met Rosemary Salvador, whose family sponsored the performances of he and his brothers. Both joined a local music group led by Charlie López, known as Orquesta Nueva (otherwise known as The Charlie López Orquesta), as vocalist and bass player, and started performing salsa at talent shows. He recorded his first song "Salsa Buena" with this band, which was followed by "Borinquen".