Ted Bishop has apologised after being sacked as president of the PGA of America for calling Ian Poulter "a little girl" on social media.
Bishop's Twitter and Facebook comments were later deleted but the PGA voted to relieve Bishop of his duties.
The PGA also apologised for Bishop's "unacceptable" and "insensitive gender-based statements".
Bishop said: "I want to apologise to Ian Poulter and anyone else that I might have offended with my remarks."
He added: "I have great remorse that my comments contained the words 'little girl' because I have always been a great advocate for girls and women in golf.
"In my 37-year career in golf, I have worked with many women to grow the sport and I have been a champion for inclusion and equal rights for women in golf.
"This is a classic example of poor use of social media on my part," added Bishop, who had one month remaining on his two-year term as the 38th PGA president.
The Ladies Professional Golf Association praised the PGA's dismissal of Bishop.
It said in a statement: "The PGA of America's quick and decisive action sent a strong message - reinforcing a consistent belief that with so many positive gains being made among golf's leading organisations, there is simply no room nor willingness, to take a step backwards."
Bishop had responded to Poulter's criticism of the Ryder Cup captaincy of Sir Nick Faldo and Tom Watson in the Englishman's new book 'No Limits'.
Englishman Faldo, who won six major titles and a record 25 Ryder Cup points during his career, drew criticism from the European team during this year's competition.
The 57-year-old, who was Europe captain at the 2008 Ryder Cup, said while commentating on this year's match that Sergio Garcia was "useless'' during the 16½-11½ loss to the United States at Valhalla six years ago, adding that he had a "bad attitude".
Poulter, 38, said in his book: "Faldo has lost a lot of respect from players because of what he said."
Noting that it was Europe's only loss in the past 15 years and that Faldo was captain, he added: "So who's useless? I think Faldo might need to have a little look in the mirror.''
In Bishop's tweet, which he later deleted, he said: "Faldo's record stands by itself. Six majors and all-time RC points. Yours vs. His? Lil Girl.''
In a separate post on his Facebook page, which was also deleted, Bishop added: "Really? Sounds like a little school girl squealing during recess. C'MON MAN!"
Poulter called Bishop's 'little girl' comments "pretty shocking and disappointing".
In a statement issued to the Golf Channel, Poulter later wrote: "Is being called a 'lil girl' meant to be derogatory or a put down? That's pretty shocking and disappointing, especially coming from the leader of the PGA of America. No further comment.''
PGA of America vice-president Derek Sprague, who has been appointed interim president, said: "The members of the PGA of America must uphold the highest standards and values of the profession, as well as the manner in which we conduct ourselves at all times.
"We apologise to any individual or group that felt diminished, in any way, by this unacceptable incident."
Bishop chose 65-year-old Watson as the 2014 US Ryder Cup captain and Poulter said in his book that Watson's decision-making "completely baffled" him, adding: "It gave us a real boost. I found it utterly bizarre."
He identified Watson's failure to play Mickelson and regular partner Keegan Bradley in either of the Saturday sessions as a particularly strange decision.
Five-time major champion Mickelson and 2011 US PGA winner Bradley won all three of their matches together at the 2012 Ryder Cup, and were also paired for the first two sessions of this year's event, winning once and losing once.