Pelagius was a Christian theologian from the late 4th to early 5th century, known for his teachings on free will and human nature. He argued that individuals have the ability to choose good or evil without the need for divine grace, emphasizing personal responsibility in moral decisions. His views were seen as controversial and led to significant debates within the early Christian church. His ideas were opposed by figures like Augustine of Hippo, who believed in the necessity of divine grace for salvation. The conflict between Pelagius and Augustine contributed to the development of Christian doctrine regarding sin, grace, and free will, influencing later theological discussions.