a night owl

Người sống về ban đêm như cú vọ

Meaning:
You're a night owl if you like to stay up and do things late at night.

Origin: Metaphorical idiom related to the fact that owls are nocturnal birds that are active at night.

For example:

She's always been a night owl. Even when she was a student she'd study late at night and get up as late as possible the next day.
I don't know why I'm a night owl. I just seem more alert at night, and even if I go to bed early I can't get to sleep till about 3 in the morning.