Don Gorske is neither an employee, nor an ambassador, nor a clinical case: he is a private individual who decided, in 1972, to eat a Big Mac a day, and kept it up. His method of proof is what got him into the book of records: he keeps the receipts.
He is regularly cited on both sides of the nutrition debate — as a counter-example to the claims of Super Size Me, or as an isolated case that proves nothing. The only established fact is the count: the record is certified, and the company had nothing to do with it.