Words were not invented by one single person, but instead words and the human language actually evolved organically, which began around 150,000 to 200,000 years ago.
Our early human ancestors and early Homo sapiens also developed sounds and gestures to be able to communicate, which then transformed gradually into the first shared vocabularies long before any history that was recorded.
The most overused word is "literally".
The word "literally" originally meant that something occurs in a strict and factual sense, although the word literally now is casually and even ironically used as an everyday emphasis for exaggerations or even metaphors.
For example, someone saying, I was literally dying of laughter at what happened to him.
Other overused words include.
Like.
Awesome and Amazing.
Synergy.
Thought leader.
Revolutionary.
And even gaslight and luxury.