Do you think a prologue MUST be used?

A prologue is a very interesting tool in novelling because it can often foreshadow events and give insight into the history of characters or introduce ideas and concepts that are used throughout the novel. However, as with all tools, prologues are a matter of personal choice. Some novels don't work well with a prologue, while some would be lost with a prologue, and some others can make do with or without. It isn't completely necessary, and I know my brother who reads a lot usually skips the prologue, so it's important not to have too much information in the prologue, however it can be used in a variety of different ways and explored.
Personally, I write fantasy, and as such if I'm going to have a prologue, I will usually have some sort of foreshadowing going on. I start it in a tone that (I hope) sounds a bit more mysterious than I would normally write it in, and usually my writing will actually develop different stylistic traits due to that. I like novels that use those kinds of prologues as well, just because it creates a nice building of suspense towards the actual story.
Hope I helped :)