A night owl is someone who tends to be awake late into the night. If you're a night owl, you may do your homework at midnight and prefer to sleep late in the morning. A night owl is often contrasted with an "early bird," or someone who naturally rises early in the morning. Night owls aren't just awake long after dark, they're also active at night, accomplishing things others do during the day. The term night owl originally meant, literally, "an owl that flies at night." Some experts credit Shakespeare with the first figurative use of night owl, in his poem "The Rape of Lucrece" in 1594.

Source: Vocabulary.com