Who created Chinese Characters? This question is for facts or historical records, not opinions. It may not be created by one person at one time, because if so, why are there so many repeated characters 通假字 or 异体字 that seem unnecessary?
Chinese characters did not all appear at once, it took countless authors, and hundreds of years to accumulate all the characters, and these characters kept evolving into today's modern Chinese characters
I am pretty sure 仓颉造字 is a myth. If such a person existed, the so-called "造字" (create characters) might just be referring to systemizing the accumulated Chinese characters at the time
The existence of 通假字 and 异体字 suggests different authors' contributions. For example, in the Warring States period, different states might write the same word differently
Cang Jie is just a mythical person.
Chinese characters started as pictograms which is pretty much like all other languages, and that took hundreds if not thousands of years. Then throughout the course of history, huge numbers of new characters emerged. So it's not possible that one single person created all the Chinese characters we have today.
In my opinion, 通假字 is actually another character that is borrowed to mean a thing at the time when the character representing the meaning is not created.
While 异体字 is probably a derivation of the same character written slightly differently by some authors in the past, it developed to become two "separate" characters.
So in conclusion the guy creating the Chinese characters did not create excess characters, but in the exact opposite, he created inadequate characters.
However, the problem of whether ChangJie invented the Chinese characters, is the job of historians, not linguists. Personally I don't think he actually existed, as he was said to have 4 eyes.
通假字：The word actually existed but the writer borrowed another word to mean the same thing for some reason
假借字：The word does not exist in the first place. And because of avoiding trouble, the writer decided to use an invented word instead of inventing a new one.
异体字：People in the past tended to simplify the writing of a word, in order to save ink. So the two or more kind of words were invented.
From above, we can see a lot of people are tending to rememebr a word by its SOUND instead of their APPEARENCE. You can google it for more info.