A close ally to Republican presidential candidate Fred Thompson resigned his post Monday as a top campaign bundler, FOX News has learned, a day after his drug-dealing history was revealed.

Phil Martin, a businessman who has lent Thompson his Cessna to fly around the country, was one of four campaign co-chairman for the '08 Republican candidate. The Washington Post reported Sunday that Martin also posted a guilty plea in 1979 for selling 11 pounds of marijuana and a no contest plea in 1983 for cocaine trafficking and conspiracy.

"I have decided to resign my position as chair of 'First Day Founders' of 'The Friends of Fred Thompson'. The focus of this campaign should be on Fred Thompson's positions on the issues and his outstanding leadership ability, not on mistakes I made some 24 years ago. I deeply regret any embarrassment this has caused," Martin said in a statement.

Thompson said Sunday that he wishes he had known earlier that one of his key presidential campaign advisers pleaded guilty to drug charges but he still thinks Phil Martin is "a good man."

Thompson, who's not the first candidate this year to be linked to a donor with a criminal past, seemed at first to brush off the news.

"You are talking about something that happened in his life, I guess, 25 years ago ... when he was in his 20s," Thompson said. "I wish I had known about it a little bit earlier. Phil, I am sure, knows that he should have told me about this. That he thought (it) was over and done with and forgotten about I am sure. But of course nothing is ever over and done with and forgotten about in this business."

Click here to see Thompson's remarks about his friend.

Martin never want to jail on the charges. Sentencing was withheld on the first plea while Martin served out probation. The 1983 charges, along with a felony bookmaking charge, came while he was still serving that probation. Martin's probation was extended, according to the Post.

Martin started out in Republican politics in Tennessee in the early 1990s, when he met GOP Rep. Zach Wamp. During fundraisers for Wamp, Martin got to know Thompson. He began donating to Thompson in 1994, during Thompson's first run for the U.S. Senate. Overall, from 1992 to 2002, Martin donated more than $75,000 to Republican candidates and causes in Tennessee, the newspaper says.

The Post reports that Martin has lent Thompson his plane for possibly two dozen campaign stops since the summer, for a price of $102,330. That's about half of what it would cost to rent a charter plane for those flights. The payment at a fraction of the commercial price was legal and common for many candidates until Congress passed lobbying and ethics reform rules in September.

Thompson said Sunday that none of the donations were improper, and the campaign has made no indication that it will return any of the money raised by Martin.

FOX News' Serafin Gomez contributed to this report.