The phrase "dark past" refers to the negative or troublesome aspects of someone's personal history or past experiences. It suggests that the person has been involved in difficult, possibly harmful or illegal activities in the past. Full definition
Not all adopted dogs come with dark pasts, and not all adopted dogs have behaviors that can be waved away or excused because of previous experiences. (mnn.com)
It sets a dark tone with the talk of a past and possibly still ongoing war, and forces the player to question the morality of said war while also hinting at the possible and equally dark past of the protagonist. (glitchcat.com)
Can Po find inner peace and accept his own dark past in time to help ward off Shen's attack? (bigpicturebigsound.com)