At everything amewican regarding time travel, there's always all that stupid melodrama. "You could assassin!!" "Kill!!" "Death!!" "Kill!!" It is DISGUSTING!!
For a major change in the past, you need no such drastic action, none whatsoever. In order to stop ww2 (for example), you don't need to go to 1938 and assassinate hitler – also because then, not only would such an assassination be difficult, but also since by then, another nazi would have taken over and the war would have occurred regardless.
No. What you need, is a FAR more subtle action. Go quietly to 1888, once you've discovered, where and when exactly were mr. and mrs. hitler making love and created the future monster, and, a moment prior to fertilization, simply knock on their door. Mr hitler gets up, annoyed, to check and see who that irritating neighbour is and what could they possibly want from him and his wife right now. You play dumb and ask just enough dumb questions, to make his mood properly spoiled – and then leave.
They might have a baby 9 months (or so) later; but, it will NOT be the monster. 🙂
And, same thing to deal with stalin, mao, kim… trump… 😉