Persia is the former name of Iran. The Persian Empire, founded by Cyrus the Great in the 6th century BC, was the largest empire of the ancient world, stretching from the borders of India and China in the east to large parts of Greece and Libya in the west. In the 4th century BC, Persia was conquered by Alexander the Great, who largely adopted Persian culture, and was subsequently ruled by Greeks before it was conquered by the Iranian Parthian tribe a century later.
In the 1st century BC, the Persian Empire came into conflict with the Roman Empire following the Battle of Carrhae where the Parthians inflicted one of the worst defeats on the Romans. This conflict continued for centuries up until the 7th century AD, when the Arab tribes conquered the entire Persian Empire and most of the Eastern Roman Empire. Persia soon became a province of the new Arab Empire, under which most Persians eventually adopted the Islamic religion. Under the new empire, the Persians made major advances in the arts and sciences, including major advances in technology, mathematics, medicine, chemistry, and philosophy. Persia eventually seperated from the Arab Empire a few centuries later, but was then invaded by Genghis Khan in the 13th century. After a century of rule by Persianized Turko-Mongol rulers, Persia eventually became an independent state and has remained as such through to the present day, now under the name Iran.
In video games, the Prince of Persia series takes place in Persia, of which the titular character is the Prince.