Octavia E. Butler

People who think about time travel stories sometimes think that going back in time would be fun because you would have all the information you needed to be much more astute than the people there, when the truth is of course you wouldn't.

Many of Judy Blume's books - which I devoured when I was growing up and where I found characters that were believable because they were a lot like me - caused considerable consternation when they were first published, but now they're widely accepted as an essential part of the children's literary canon.