Villains who are biologically relatives Heroes or any major protagonists, they can be parents, siblings, grandparents, ancestors, uncles/aunts, cousins, children, grandchildren, nephews/nieces, descendants, distant relatives, or even clones of heroes.

This is a common trend in fiction in an attempt to add drama and to a lesser extent, irony to the story. Indeed, having to fight a close relative is a source of much inner turmoil to the hero who cannot reconcile their quest and familial ties. Often, this results in the villain attempting to turn the hero over to their side. Other times, the opposite will occur and the hero will attempt to turn the villain back to their side, which can eventually lead to redemption. (The perfect example of this is of course, Darth Vader, Eurus Holmes from the BBC Series Sherlock who is biologically related to the protagonist Sherlock Holmes.)