I have a question related to oxidizing agents. Why do some oxidizing agents have to be in acid medium?

For example the potassium permanganate.
I would also like to know if there are other examples of oxidizing agents that have to be in acid medium or where I can find them.

Some work better in acid medium, some work better in alkaline medium and some, permanganate for example work differently in acid and base.

MnO4^- is reduced to Mn^2+ in acid medium but to MnO2 in basic medium.