来历不明的人
people of dubious origins
这人的来历我不大清楚。
I'm not clear about this person's background.
日子长了我才知道他这个外号的来历。
It was only after a long time that I understood where his nickname came from.
他马上意识到这老头儿一定有些来历。
He immediately realized that the old guy had a long story behind him.
此人大有来历。
This person has a long history.
这自有它的来历。
This has its own background.
提起这面红旗，可大有来历。
You brought up the red flag, well there's a long story behind that.