In this time travel trope, a character goes back in time and (usually accidentally) replaces their own grandfather (or similar relative). Often this involves having sex with their grandmother, sometimes it involves killing their grandfather, preventing their grandparents from ever meeting or falling in love, etc. It's typically interpreted as a form of Stable Time Loop but such an interpretation may be stretching the laws of genetics (if not causality).
The term can also refer more generally to the idea of a time traveler doing anything that prevents their own existence or birth, or that prevents their need (or ability) to travel back in time in the first place.
Game and Story Use
- Many games set Player Characters a step above the rest, making them special heroes that the norms and mundanes can't hope to compete with. One particularly disturbing way of making this distinction meaningful in a time travel game would be to establish that all the PCs came about as a result of the Grandfather Paradox. Perhaps the presence of a Stable Time Loop in your recent genetic history somehow makes a person more powerful or special.
- One way of making a villain especially distasteful (and a little pathetic or even humorous if you're not careful) would be to establish that they'd willingly and intentionally been their own Grandfather. This may even be a diagnosable form of mental disorder in a setting where time travel is commonplace.