[Gideonwoulfe]

I think he meant Heinlein was the essential Science fiction writer.

[Moltke]

On further thought, neither 'non plus ultra' (unsurpassed, "last word (in) (the very best)") nor 'sine qua non' ("an essential or indispensable element, condition, or ingredient") properly applies to a person.

Sorry, I just notice when such terms are misused or mangled (e.g. 'ad nauseum' instead of 'ad nauseam'). I'll shut up now. ;-)