Hertz Global Holdings CEO Mark Frissora resigned last week, reflecting what analysts see as shareholder dissatisfaction with operational issues, ranging from a recent shortage of airport vehicles to the slower-than-expected integration of its Dollar Thrifty division.

While Hertz on Sept. 8 would only cite "personal reasons" for Frissora's departure, the No. 2 U.S. car rental company was tripped up during the second quarter by vehicle recalls, which reduced its on-airport inventory and increased lower-rate, off-airport rentals as a percentage of total rentals. That, combined with an aging fleet and accounting issues that have prevented the company from releasing any financial results this year, spurred activist investors led by Carl Icahn to push out Frissora after eight years on the job.

"Hertz is more of a multiyear turnaround story at this point, one that will require significant investment in people and [importantly] technology," Deutsche Bank analyst Chris Woronka wrote in a Sept. 8 note to investors. "The near-term priority is to prevent slippage in brand equity given the operational challenges that produced a shortage of rentable vehicles on-airport during [the second quarter]."

Frissora was named CEO of Hertz in July 2006 and took the company public later that year. He also oversaw a two-year bidding war against Avis Budget for smaller competitor Dollar Thrifty Automotive Group, more than doubling the price offered for Dollar Thrifty before securing the $2.6 billion acquisition in 2012.

Hertz also grew by debuting services such as Hertz 24/7. A model that combines keyless entry capabilities with self-service and hourly rentals, Hertz 24/7 reflected an effort to take on rapidly growing car-sharing companies such as Zipcar, which was acquired by Avis Budget last year.

Overall, Hertz generated $10.8 billion in revenue last year, up 24% from $8.69 billion in 2007, Frissora's first full year overseeing the company. And with Dollar Thrifty under its wing, Hertz last year accounted for about a quarter of the $24.5 billion U.S. car rental market, second only to Enterprise Holdings' 48%, according to trade publication Auto Rental News.

Still, such growth created challenges. This year, Hertz failed to report either first- or second-quarter financial results because of accounting issues that dated back three years.

Then, last month in a Securities and Exchange Commission filing, Hertz said revenue would be "well below the low end of its 2014 guidance," in part because second-quarter vehicle recalls jumped while business bookings spiked, causing fleet shortages.

Following that admission, both Deutsche Bank and JP Morgan downgraded Hertz's stock while activist investor Carl Icahn acquired 8.5% of the company, both spurring and reflecting dissatisfaction with the company's operations and stock performance.

For the year prior to Frissora's departure, Hertz's stock rose 12% while Avis Budget's more than doubled.

Frissora was replaced on an interim basis by Brian McDonald, CEO of the company's Hertz Equipment Rental Corp., while the company's board searches for a successor.

"Hertz has shown extraordinary results that many CEOs would give their left arm to achieve," said car rental industry consultant Neil Abrams, a former Hertz executive. "But Frissora has failed to move the stock value. And once Icahn gets involved, there's trouble ahead."

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