T. Michael Glenn, who ran sales and marketing for FedEx Corp. and was one of the transportation industry's most influential executives over the past 25 years, will retire on Dec. 31, the company said yesterday. The announcement triggered some of the most sweeping changes to affect the company's top hierarchy in recent memory.

Glenn, 61, officially retires as executive vice president, market development and corporate communications, which was a newly created position when he assumed it in 1998. But the title understates the sweeping nature of his responsibilities and his impact on Memphis-based FedEx's evolution. Glenn led the company's marketing, sales, customer service, and communications groups. He guided the company's sales, marketing, and communications through its dramatic expansion into the ground parcel, less-than-truckload (LTL), and logistics segments, as well as its overseas expansion. Glenn is also the head of the company's revenue management committee.

David J. Bronczek, CEO of FedEx Express, the company's air and international unit, will assume the new post of president and chief operating officer of parent FedEx Corp. on Jan. 1, 2018. On Jan. 1, 2017, Bronczek will replace Glenn as chairman of the revenue management committee.

As the parent's president, Bronczek would replace founder Frederick W. Smith, who has served as chairman and CEO as well as president. The company did not detail Bronczek's new responsibilities in its statement, nor did it announce who would succeed Bronczek at FedEx Express.

In addition, Robert B. Carter, currently chief information officer and co-CEO with Glenn of FedEx Services, the company's primary internal support unit, will become the unit's sole CEO effective Jan. 1. Carter will oversee the administration of common information technology, sales, solutions, marketing, and corporate communications for all of FedEx's operating companies, according to the company.

FedEx's top executive team is comprised of five people, including Smith and Carter, who've been in their respective positions for years. The other members are Glenn, CFO Alan B. Graf, Jr., and Christine P. Richards, FedEx's general counsel.

In his role, Glenn was effectively the transport and logistics giant's number-two executive, with only Smith above him on the organizational chart.

In a statement, Smith paid what was perhaps the ultimate tribute to Glenn, calling him the "most brilliant marketer" Smith has ever known, and saying "our company, brand, and portfolio would not be anything close to what it is today" without him.

Glenn, a 35-year FedEx employee, is leaving the company to spend more time with his family, the company said.