"We will not be writing any further checks," Mr. Mars wrote. "Your performance as a manager is lacking. As a historian and archivist, etc., you excel. You have not given proper supervision and leadership to the staff."
Mr. Mars said he and his wife paid for most of the Mars Education Center.
"As far as the new center, I would think that besides not communicating with your president (Mrs. Mars) regarding the opening of it, the exhibits to be in it, the budget for operating it and a program for the future use, you might have been nice enough and polite enough to communicate with the major donor (Mr. Mars). Not a word from you to either of us. We do not even know if you can fund it."
The letter also said Mr. Mars had paid for one of Westbrook's sons to attend an elite private school and had paid for exotic vacations for Westbrook and his wife.
Westbrook said he won't comment specifically on Mr. Mars's letter but wishes either of them had discussed their issues with him before sending it.
Without releasing exact amounts, Westbrook said it's important to know the Marses were not the only contributors to the new Education Center.
"It was due to the tremendous generosity of Forrest and Deborah Mars and 350 other donors. When we started, some members of our board thought that we'd be fortunate to raise $2 million."
The building might bear Deborah Mars's name, but many other people helped, Westbrook said.
"This project has opened a lot of doors for us over the last five years."
He said Mrs. Mars originally stood up at an 18th-century-style officers' dinner at the fort and offered the Education Center as a gift.
"I think Forrest and Deborah had in mind a transformational gift. They challenged us to become a year-round operation, extending our reach into the wider world and finding new ways to be relevant to audiences of all kinds."