Identity. It's not just a good idea - it's the Law.
So, based on further discussions and research...
Parmenides was the first to say
Something resembling A is A.
"Never shall this be proved - that things that are not, are."
In the middle ages,
"All a is a" was used by sages.
The monks were using letters as terms in the study of logic, and some of them thought this was a fine premise.
Leibniz still gets the tap
As the guy who put "A is A" on the map.
It was he who made a big deal of "A is A", putting it forth as a catchy statement of the law of identity.
About these conclusions, I'm not too smug.
I may learn some cave man said "Ug is Ug."