American Airlines is set for a leadership shakeup.CEO Doug Parker announced on Tuesday that he will retire on March 31, paving the way for current American Airlines President Robert Isom to take over as CEO.Parker’s retirement will cap a run in which he reshaped both American – and the U.S. airline industry as a whole – in his role as a chief executive.Want more airline-specific news? Sign up for TPG’s free new biweekly Aviation newsletter!Parker’s first stint as CEO came at America West, where he took over the top spot in 2001 – just before the 9/11 terrorist attacks set the industry on its heels.Parker guided the Phoenix-based low-cost carrier through that crisis, and then set the airline on a course that would dramatically alter the landscape of the U.S. aviation industry.Next came a merger with East Coast-based US Airways.Parker’s America West was the acquiring carrier, but his airline assumed the more-widely recognized brand of US Airways. The 2005 deal transformed America West, now US Airways, into a national player that had hubs across the U.S. – notably in Phoenix, Charlotte and Philadelphia. Two other landmark hubs of the combined company — Las Vegas and Pittsburgh — would ultimately be dropped in the 2000s.There was still one more acquisition to come.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.That came in 2012 with a shocking bid by US Airways to acquire much larger American Airlines, which was then reorganizing in Chapter 11 bankruptcy protection. American initially was cool to the deal, but Parker’s team won over labor groups at American in a move that eventually paved the way for a deal to proceed a year later after forcing American’s management team to the table.The American-US Airways merger closed in 2013, with Parker’s airline again taking the name of the better-known brand of its new partner.The tie-up came after a wave of consolidation had swept through the U.S. industry. Four big mergers that were announced between 2008 and 2013– United-Continental, Delta-Northwest and Southwest-AirTran – reshaped the competitive landscape of the U.S. market.But it was American’s merger with US Airways that left it as the world’s biggest airline. And soon – for the first time since that 2013 deal – the carrier will be turning to a new leader to go forward.“I’m extraordinarily excited about the future of American with Robert as our next leader,” Parker said in a Tuesday morning letter to employees. “I have no doubt that the best is yet to come for American, and no one will be cheering louder for all of you than I will.”