Daniel appears to have many authors.
Excerpt:
The original purpose of the Book of Daniel was to comfort and encourage persecuted Jews during the Maccabean revolt. It all began in December of 167 BC, when the Seleucid emperor Antiochus Epiphanes desecrated the Temple in Jerusalem with an idol bearing his likeness. He went on to force his Jewish subjects to abandon the Sabbath, circumcision, and food laws, torturing and killing all who opposed him. At this outrage, the Jews revolted under Judas Maccabeus, driving the Seleucid armies out of Palestine and recapturing the Temple. In December of 164 BC, they rededicated the Temple to Jewish worship on the first Hanukkah.
During the revolt, pious Jews began to circulate an anthology of stories allegedly written four hundred years earlier by a Jewish hero named Daniel.
These stories relate how Daniel and his friends, while serving as officials in the courts of pagan kings, risked their lives to avoid breaking Jewish food laws or worshipping false gods. When the mightiest kings on Earth tried to force them to compromise their religious principles, they passively waited on God's miraculous intervention to save them. The success of Daniel's prophecies of events up to and including the atrocities of Antiochus supposedly demonstrated that God would miraculously intervene on schedule to rescue the Jews from Antiochus as well.
The prophet Daniel supposedly predicted that four great empires were to rise and fall in succession between his day and the end of the world: Babylonia, Media, Persia, and Greece. Alexander the Great's Greek Empire was to break up into four smaller empires, the most important being the Seleucid Empire in Syria to the north, and the Ptolemaic Empire in Egypt to the south.
After seven Greek kings ruled in succession, the eighth was to snatch the throne from three candidates who had more right to it than he did. This king, Antiochus Epiphanes, provoked the Maccabean War.
The Book of Daniel predicted that God would miraculously destroy Antiochus Epiphanes, resurrect the righteous dead, and set up an everlasting, worldwide Israelite Empire three and a half years after the desecration of the Temple; in other words, the Messianic Empire should have begun in June of 163 BC.
Since these predictions largely came true until the middle of the war and failed thereafter, we know that the author lived in Seleucid times, not Babylonian times.
The Failure of Daniel's Prophecies