This was a common name in classical Greece, and, due to both the saints who carried it and the favourable meaning, it came into general use in the Christian world, being especially popular among Eastern Christians. It was however rare in Britain before the 19th century. Famous bearers include three tsars of Russia (in the Russian form Fyodor) and American president Theodore Roosevelt (1858-1919).
This name was popularized in continental Europe by the works of the 18th-century Scottish poet James Macpherson [1]. Napoleon was an admirer of Macpherson, and he suggested Oscar as the second middle name of his godson, who eventually became king of Sweden as Oscar I. Other notable bearers include the Irish writer and humorist Oscar Wilde (1854-1900) and the Brazilian architect Oscar Niemeyer (1907-2012).
In England Oliver was a common medieval name, however it became rare after the 17th century because of the military commander Oliver Cromwell, who ruled the country following the civil war. The name was revived in the 19th century, perhaps due in part to the title character in Charles Dickens' novel Oliver Twist (1838), about a poor orphan living on the streets of London. It became very popular at the beginning of the 21st century, reaching the top rank for boys in England and Wales in 2009 and entering the top ten in the United States in 2017.
Due to the renown of the saint, this name has been widely used in the Christian world. It has been common in England since the 12th century, though it became a bit less popular after the Protestant Reformation. The name has been borne by five popes and two tsars of Russia.