The special case of Bootstrap Paradox in which a guy travels back in time to protect himself is common these days. I have encountered it countless times.
The first example I encountered was in Shaktimaan (late 90s) Episode 227 (jump to 24:11) in which the superhero travelled back in time to protect his mother and his child-self from his arch nemesis Kilvish.
The most recent I encountered:
In The Flash (2014) TV series, Flash from the future travelled back in time to protect his child-self from Reverse Flash.
Which Sci-Fi work introduced this idea to the world?
timelinetag is inappropriate. In Bootstrap Paradox, timeline remains same.