(This is quite a speculative fiction-specific peeve).
Lazily using historical figures to illustrate just how wondrous the organisation the protagonist is being inducted into is.
‘Yes, we are naturally cleverer than normal human beings. Einstein was one of us. So was Leonardo Da Vinci, and many of the great thinkers in human history’.
It’s not to say that the retconning of history can’t be done well, but it’s usually so clumsy, and unnecessary.