Strictly speaking, every science fiction tale presents its own version of future and therefore there are as many science fiction universes as there are science fiction stories. Many SF tales follow dictates of a particular subgenre like Cyberpunk or Space Opera of which, see the separate entry.
... who assumed power for any period of time without a legitimate basis of authority.
The first to have the title of "Tyrant" was Pisistratus in 560 BC.
In modern ...