Pinochet, for one. US-backed coup d'etat overthrowing a democratically-elected government. For more you can read the Wikipedia article United States involvement in regime change
Lenin - 200k executions, 5 million deaths due to famines
Stalin - 800k executions, 1.7 million deaths in the Gulag, plus some famine and some miscellaneous brings to around 5million, some estimates upwards 20 million.
https://en.wikipedia.org/wiki/United_States_involvement_in_r...