Who, whoever, anyone. All of these can be used to translate the Slovak pronoun "kto" - so in fact it's the Slovak word that is tricky today, because you have to be sure about how it is used each time you see or hear it. "Kto?" in a question is "Who?" (so is "Koho?", "O kom?", "S kým?", "Komu?" - but check the subject [1. pád] of the question!).

"Človek/Osoba/Ľudia, ktorý/á/í" are also all "who" in English ("which" is for things, objects). A Slovak sentence starting "Kto chce, sa môže pozerať..." is not a question, and in English this should start "Whoever wants…" or "Anyone who wants…", because in fact the Slovak meaning is "Ktokoľvek chce...". Questions about the past, finding out who did what, like "Kto nechal dáždnik ...", must start with "Whoever left their umbrella…", because the owner is a specific person, not just anybody.