Daniel was not so much a teacher as a representative of God's people in a pagan land. His prophecies may have helped the Jewish people during the time of Antioch Ephiphanes in the days of the Maccabees, but the Bible does not confirm this.
1 Maccabees 2:59 Ananias, Azarias, and Misael, by believing were saved out of the flame. 60 Daniel for his innocency was delivered from the mouth of lions. 61 And thus consider ye throughout all ages, that none that put their trust in him shall be overcome.
International Standard Bible Encyclopedia.
dan´yel (דּניּאל, dānīyē'l, דּנאל, dāni'-ēl, “God is my judge”; Δανιήλ, Daniḗl):
(1) One of the sons of David (1Ch_3:1).
(2) A Levite of the family of Ithamar (Ezr_8:2; Neh_10:6).
(3) A prophet of the time of Nebuchadnezzar and Cyrus, the hero and author of the Book of Daniel.
1. Early Life
We know nothing of the early life of Daniel, except what is recorded in the book bearing his name. Here it is said that he was one of the youths of royal or noble seed, who were carried captive by Nebuchadnezzar in the third year of Jehoiakim, king of Judah. These youths were without blemish, well-favored, skillful in all wisdom, endued with knowledge, and understanding science, and such as had ability to stand in the king's palace. The king commanded to teach them the knowledge and tongue of the Chaldeans; and appointed for them a daily portion of the king's food and of the wine which he drank. After having been Thus nourished for three years, they were to stand before the king. Ashpenaz, the master or chief of the eunuchs, into whose hands they had been entrusted, following a custom of the time, gave to each of these youths a new and Babylonian name. To Daniel, he gave the name Belteshazzar. In Babylonian this name was probably Belu-lita-sharri-usur, which means “O Bel, protect thou the hostage of the king,” a most appropriate name for one in the place which Daniel occupied as a hostage of Jehoiakim at the court of the king of Babylon. The youths were probably from 12 to 15 years of age at the time when they were carried captive. (For changes of names, compare Joseph changed to Zaphenath-paneah (Gen_41:45); Eliakim, to Jehoiakim (2Ki_23:34); Mattaniah, to Zedekiah (2Ki_24:17); and the tw names of the high priest Johanan's brother in the Sachau Papyri, i.e. Ostan and Anani.)
Having purposed in his heart that he would not defile himself with the food and drink of the king, Daniel requested of Ashpenaz permission to eat vegetables and drink water. Through the favor of God, this request was granted, notwithstanding the fear of Ashpenaz that his head would be endangered to the king on account of the probably resulting poor appearance of the youths living upon this blood-diluting diet, in comparison with the expected healthy appearance of the others of their class. However, ten days' trial having been first granted, and at the end of that time their countenances having been found fairer and their flesh fatter than the other youths', the permission was made permanent; and God gave to Daniel and his companions knowledge and skill in all learning and wisdom, and to Daniel understanding in all visions and dreams; so that at the end of the three years when the king communed with them, he found them much superior to all the magicians and enchanters in every matter of wisdom and understanding.
Daniel's public activities were in harmony with his education. His first appearance was as an interpreter of the dream recorded in Dan 2. Nebuchadnezzar having seen in his dream a vision of a great image, excellent in brightness and terrible in appearance, its head of fine gold, its breast and its arms of silver, its belly and its thighs of brass, its legs of iron, its feet part of iron and part of clay, beheld a stone cut out without hands smiting the image and breaking it in pieces, until it became like chaff and was carried away by the wind; while the stone that smote the image became a great mountain and filled the whole earth. When the king awoke from his troubled sleep, he forgot, or reigned that he had forgotten, the dream, and summoned the wise men of Babylon both to tell him the dream and to give the interpretation thereof. The wise men having said that they could not tell the dream, nor interpret it as long as it was untold, the king threatened them with death. Daniel, who seems not to have been present when the other wise men were before the king, when he was informed of the threat of the king, and that preparations were being made to slay all of the wise men of Babylon, himself and his three companions included, boldly went in to the king and requested that he would appoint a time for him to appear to show the interpretation, Then he went to his house, and he and his companions prayed, and the dream and its interpretation were made known unto Daniel. At the appointed time, the dream was explained and the four Hebrews were loaded with wealth and given high positions in the service of the king. In the 4th chapter, we have recorded Daniel's interpretation of the dream of Nebuchadnezzar about the great tree that was hewn at the command of an angel, Thus prefiguring the insanity of the king.
3. Interpreter of Signs
Daniel's third great appearance in the book is in chapter 5, where he is called upon to explain the extraordinary writing upon the wall of Belshazzar's palace, which foretold the end of the Babylonian empire and the incoming of the Medes and Persians. For this service Daniel was clothed with purple, a chain of gold put around his neck, and he was made the third ruler in the kingdom.
4. Seer of Visions
Daniel, however, was not merely an interpreter of other men's visions. In the last six chapters we have recorded four or five of his own visions, all of which are taken up with revelations concerning the future history of the great world empires, especially in their relation to the people of God, and predictions of the final triumph of the Messiah's kingdom.
5. Official of the Kings
In addition to his duties as seer and as interpreter of signs and dreams, Daniel also stood high in the governmental service of Nebuchadnezzar, Belshazzar, and Darius the Mede, and perhaps also of Cyrus. The Book of Dnl, our only reliable source of information on this subject, does not tell us much about his civil duties and performances. It does say, however, that he was chief of the wise men, that he was in the gate of the king, and that he was governor over the whole province of Babylon under Nebuchadnezzar; that Belshazzar made him the third ruler in his kingdom; and that Darius made him one of the three presidents to whom his hundred and twenty satraps were to give account; and that he even thought to set him over his whole kingdom. In all of these positions he seems to have conducted himself with faithfulness and judgment. While in the service of Darius the Mede, he aroused the antipathy of the other presidents and of the satraps. Unable to find any fault with his official acts, they induced the king to make a decree, apparently general in form and purpose, but really aimed at Daniel alone. They saw that they could find no valid accusation against him, unless they found it in connection with something concerning the law of his God. They therefore caused the king to make a decree that no one should make a request of anyone for the space of thirty days, save of the king. Daniel, having publicly prayed three times a day as he was in the habit of doing, was caught in the act, accused, and on account of the irrevocability of a law of the Medes and Persians, was condemned in accordance with the decree to be cast into a den of lions. The king was much troubled at this, but was unable to withhold the punishment. However, he expressed to Daniel his belief that his God in whom he trusted continually would deliver him; and so indeed it came to pass. For in the morning, when the king drew near to the mouth of the den, and called to him, Daniel said that God had sent His angel and shut the mouths of the lions. So Daniel was taken up unharmed, and at the command of the king his accusers, having been cast into tile den, were destroyed before they reached the bottom.