What trope would this example be?

I've been looking around and can't quite seem to find a trope that fits this:

Protagonist gets surprised by a masked person, who shoves him through a portal/puts a teleportation device on him/sends him to the past/etc. Protagonist goes on adventure, grows older, becomes a hero, etc. Eventually, he travels back in time and dons a mask, ambushes his past self, and starts the adventure.

Essentially, stable time loop where the protagonist's future self is the instigator of the story.

Thoughts?

Please try Trope Finder, as it says above.