I am creating a document to list "Complaints and Compliments" by customers/suppliers/staff/anyone, I want a column heading preferably a single word do describe the person making the compliment or complaint. The column will contain their name.
Try originator. From Collins:
countable noun [usu with poss]
The originator of something such as an idea or scheme is the person who first thought of it or began it.
...the originator of the theory of relativity.