The Roman Martyrology for July 21st commemorates "at Babylon, the holy prophet Daniel" (and, incidentally, on July 20th the Prophet Elijah was commemorated).
Daniel is perhaps most popularly known by way of the Bible story of "Daniel in the Lions' Den", taken from the Book of Daniel 6:10-23:
When Daniel knew that the document had been signed, he went to his house where he had windows in his upper chamber open toward Jerusalem; and he got down upon his knees three times a day and prayed and gave thanks before his God, as he had done previously. Then these men came by agreement and found Daniel making petition and supplication before his God. Then they came near and said before the king, concerning the interdict, "O king! Did you not sign an interdict, that any man who makes petition to any god or man within thirty days except to you, O king, shall be cast into the den of lions?" The king answered, "The thing stands fast, according to the law of the Medes and Persians, which cannot be revoked." Then they answered before the king, "That Daniel, who is one of the exiles from Judah, pays no heed to you, O king, or the interdict you have signed, but makes his petition three times a day." Then the king, when he heard these words, was much distressed, and set his mind to deliver Daniel; and he labored till the sun went down to rescue him. Then these men came by agreement to the king, and said to the king, "Know, O king, that it is a law of the Medes and Persians that no interdict or ordinance which the king establishes can be changed." Then the king commanded, and Daniel was brought and cast into the den of lions. The king said to Daniel, "May your God, whom you serve continually, deliver you!" And a stone was brought and laid upon the mouth of the den, and the king sealed it with his own signet and with the signet of his lords, that nothing might be changed concerning Daniel. Then the king went to his palace, and spent the night fasting; no diversions were brought to him, and sleep fled from him. Then, at break of day, the king arose and went in haste to the den of lions. When he came near to the den where Daniel was, he cried out in a tone of anguish and said to Daniel, "O Daniel, servant of the living God, has your God, whom you serve continually, been able to deliver you from the lions?" Then Daniel said to the king, "O king, live for ever! My God sent his angel and shut the lions' mouths, and they have not hurt me, because I was found blameless before him; and also before you, O king, I have done no wrong." Then the king was exceedingly glad, and commanded that Daniel be taken up out of the den. So Daniel was taken up out of the den, and no kind of hurt was found upon him, because he had trusted in his God.
Those who pray the Divine Office will be particularly familiar with a canticle which is taken from the Book of Daniel related to the three holy youths, Ananias, Azarias and Misael, the Canticum trium Puerorum or Benedicite: "Bless the Lord, all you works of the Lord; Praise and exalt him above all forever..."
Aside from the Divine Office, on Sundays and Feast days in the Mozarabic rite the "Hymnus Trium Puerorum" (an abridged form of the same canticle) was also sung. (See an image of the chant from the Mozarabic Missal.) Here is that Mozarabic chant:
