Normally when this is asked, people think about reviving, curing, resurrecting. This question is about who you save if you were transported to a time a little before their death, like maybe a day before or even a week before. Anything about terminal illnesses or diseases contracted don’t really count here because, when those things happen, they happen and there’s really nothing you could do to have prevented it.
I think I would’ve wanted to prevent JFK’s assassination. I’d tell him “dude, do not get in that limo and drive down Elm Street” and I’d show him a newspaper clip of the day of his assassination. I’d probably be looked at a little crazily and suspected of maybe being involved in something that pertains to that day. But, it’s an effort I would’ve gone through to do that.


Have you watched the Stephen King movie about that?
Or better yet, read the book that the “movie” (it’s a miniseries) was based on? Both are called 11/22/63, but the book is much better.
Second this recommendation, the book is fantastic. I didn’t finish the TV miniseries as they changed too much for my taste.