Basilides of Alexandria was a Christian teacher and philosopher active in the Egyptian city of Alexandria during the 2nd century CE, under the Roman emperors Hadrian and Antoninus Pius. He is considered one of the earliest and most important figures in the Gnostic tradition, a movement that sought special spiritual knowledge. He founded a school in Alexandria, and his son Isidore was also part of his intellectual circle.

His major work was a 24-volume commentary on the Christian Gospel titled the Exegetica. This work, along with any others he may have written, is lost. Our knowledge of his ideas comes entirely from fragments quoted by later Christian critics who opposed his teachings. According to these sources, Basilides developed a complex system that blended Christian concepts with Greek philosophy. His system described a hierarchy of divine beings and made a sharp distinction between the supreme, unknowable God and a lower creator god responsible for the material world. Modern scholars see him as a foundational thinker who represented a significant early attempt to create a comprehensive philosophical theology from diverse traditions. Because his work survives only through the writings of his opponents, reconstructing his authentic thought remains a major challenge for historians.