I have looked at the Emperor as a kind of Ulitharid. Not quite the same but possibly a missing link between the two types.

https://forgottenrealms.fandom.com/wiki/Ulitharid

Here are two wikis for those that aren’t sure of the details of mindflayers:

https://en.wikipedia.org/wiki/Illithid

https://forgottenrealms.fandom.com/wiki/Mind_flayer