St. Eusebius of Vercelli was a Christian bishop in the 4th century, known for his strong opposition to Arianism, a belief that denied the divinity of Christ. He served as the Bishop of Vercelli, a city in northern Italy, and played a significant role in the early Church's efforts to define orthodox Christian beliefs. Eusebius was a prominent figure at the First Council of Nicaea in 325 AD, where he defended the Nicene Creed against Arian teachings. He was later exiled for his beliefs but continued to advocate for the unity of the Church until his death around 371 AD. His legacy is celebrated in the Roman Catholic Church and other Christian traditions.