MILAN (AP) — Sergio Marchionne's achievements as one of the automotive world's most charismatic chief executives include the bold trans-Atlantic merger of Italian carmaker Fiat and U.S. No. 3 Chrysler after he restored both to health.

But Marchionne told analysts during a big presentation last month that his true legacy at Fiat Chrysler Automotive would be the culture of a corporation where "mediocrity is never, ever worth the trip."

The Italian-Canadian always insisted a replacement would come from the ranks of his hand-picked and tested team, managers who met his exacting standards. Asked if he planned to leave a script behind if he stepped down next year as planned, Marchionne said that wouldn't be necessary.

"There is no script or instructions. Instructions are institutional and temporary," he said. "FCA is a culture of leaders."

Marchionne, 66, was hastily replaced as CEO of Fiat Chrysler on Saturday after the company announced that his health had taken a turn for the worse following shoulder surgery last month in Zurich, Switzerland. Details of the complications and his condition have not been released, but the company said they prevented him from returning to work.

Marchionne was replaced by the head of Jeep and Ram, Mike Manley. The Briton was a key executive on Marchionne's team, growing the quintessentially American Jeep brand into a global marquee.

Fiat Chairman John Elkann, in a letter to Fiat's 236,000 employees Sunday, called Marchionne a "true, rare kind of leader" and lauded him as "the best CEO that anyone could ask for and to me personally, a true mentor, partner, close friend."

Elkann, the 42-year-old heir to the Agnelli family that founded the Italian carmaker Fiat in 1899, remembered Marchionne's arrival in 2004 at "one of the darkest moments" for the long-struggling company.

"It was his intellect, perseverance and leadership that saved Fiat," Elkann wrote in the letter. "He taught us to have the courage to challenge the status quo, to break with convention and go beyond the tried and tested."

The Fiat-Chrysler merger remains the crown jewel in the 14-year Marchionne era, an accomplishment built on a series of daring plays.

In 2005, the trained lawyer who studied philosophy demonstrated his deal-making skill by getting GM to pay $2 billion to sever ties with Fiat as part of a failed cross-border tie-up. The money was pivotal to relaunching the failing carmaker.

Then in 2009, he secured a deal with a then-new U.S. President Barack Obama to take over bankrupt Chrysler without Fiat having to put a penny down in exchange for Fiat's small car technology.

Other essential corporate moves included the spin-off of the heavy industrial vehicle and truck maker CNH and of the Ferrari supercar maker. Both deals unlocked considerable shareholder value for Agnelli family heirs.

But his ambition to complete another big deal, this one a merger with U.S. carmaker GM, failed.

Marchionne also has been replaced as CEO of Ferrari and chairman of CNH Industrial. He had planned to update the financial community on his 5-year plan for the super sports car maker in September.