The most famous example is surely Chile, 1973:
https://en.wikipedia.org/wiki/1973_Chilean_coup_d'état (which lead to Pinochet getting to power, a bloody dictator, but certainly sweet on that US money), there is also another famous murder, done by a CIA operative (
https://en.wikipedia.org/wiki/Che_Guevara#Capture_and_death, though, the target wasn't the leader of any country). Generally speaking, the US pulled a lot of shady shit in Latin America, supporting the Contras in Nicaragua for example, a group
that committed numerous human rights violations.
To give an example of an African leader being killed, there is the story of
Patrice Lumumba. Was even shot down by a Belgian firing squad during, essentially, a coup d'etat. Unsurprisingly the US also had their hands in this, after all, we couldn't risk a country slipping into Soviet zone of influence, now could we? Treading on the independece of sovereign nations was fairly common thing during the Cold War.