4 iconic American CEOs are on the way out. Meet the nuts-and-bolts leaders taking their place.

Buffett made way for Greg Abel at the start of this year, marking the end of the legendary investor’s six-decade run as Berkshire’s CEO.

Abel previously headed up Berkshire’s non-insurance operations, and before that served as CEO of Berkshire Hathaway Energy.

He’s widely seen as a more hands-on manager than Buffett, who along with the late Charlie Munger, designed Berkshire as a web of independent subsidiaries led by an army of CEOs. That structure freed up the pair to focus on big-picture capital allocation instead of day-to-day management.

Abel has signaled he’ll keep a closer eye on Berkshire’s businesses and hold accountable those that underperform. But ascending to CEO has meant adding Berkshire’s vast insurance business and investment portfolio to his remit.

Ram Charan, a veteran consultant who’s authored more than 35 books, including “Execution: The Discipline of Getting Things Done,” told Business Insider that it will be “very demanding” for Abel to allocate his time between all those responsibilities.

Charan said Abel’s success will depend on whether he can put the right CEO in charge of each subsidiary and, like Buffett, allocate capital wisely.

John Longo — a finance professor, investment chief, and the author of “Buffett’s Tips” — told Business Insider that Abel’s eye for detail and background could help him cater to the energy needs of the AI infrastructure buildout, one of the key business trends of today.

Apple announced in April that hardware boss John Ternus will succeed Cook as CEO in September.

Ternus is a mechanical engineer who’s worked at Apple for over 25 years. He oversaw the company’s shift to Apple Silicon, and the design and engineering of numerous products, including AirPods and recent generations of the iPhone.

He’s known for his obsessive attention to detail. He famously argued with a supplier late at night after using a magnifying glass to discover there were 35 grooves on the heads of the screws in a product, instead of the 25 Apple had specified.

Apple’s cofounder and former CEO, the late Steve Jobs, was also known for caring about every microscopic detail of his products, even if customers would never notice them.

In contrast, Cook’s expertise lay in supply chains and logistics. He scaled up production, unlocked the vast Chinese market, and grew Apple into one of the world’s most valuable companies.

“Building perfect products the consumer will want at hyper volumes is a special talent,” Charan said. “Jobs had the gift and a recipe. Execution of the recipe got diluted.”

However, Ternus “knows the whole recipe” of perfecting hardware, prioritizing ease of use for customers, integrating software, and hiring the world’s best engineers and other talent, Charan continued.

Asked whether Apple will launch new, groundbreaking products under Ternus, Charan replied: “Count on it.”

Doug McMillon passed the CEO mantle to John Furner in February.

Furner started his career at Walmart as an hourly store associate in 1993. Over the next 30 years, he advanced from stocking shelves to managing stores, sourcing products, overseeing marketing and merchandising, then running the entire US business.

He’s known for visiting Walmart stores and speaking to associates to identify and fix operational issues, as well as inviting them to share their stories and feedback in special forums.

“Furner’s leadership heft will drive personalization through digitization,” Charan said.

He predicted that Furner will surround himself with digital-savvy executives, and build on McMillon’s success in transforming Walmart to better compete with online rivals like Amazon.

“Count on Walmart getting ahead,” Charan said, adding that the retailer has the “consumer touch” that its rivals don’t.

Iger ran Disney for a total of 19 years across two stints as CEO, reshaping the company by acquiring Pixar, Marvel, Lucasfilm, and 21st Century Fox.

D’Amaro — who took over in March — has worked at Disney for nearly 30 years, most recently as the chief of its experiences division.

In that role, he oversaw hundreds of thousands of workers, along with hotels, restaurants, stores, attractions, transportation, and every other aspect of a complex and constantly shifting business.

D’Amaro is known to walk Disney’s parks, asking cast members and customers for their thoughts, and for relentlessly working to improve the guest experience.

Iger said in the press release announcing D’Amaro’s appointment that he possessed the “rigor and attention to detail” needed to be Disney’s CEO, and combined “creativity with operational excellence.”

D’Amaro is the “right man” for the job, Charan said, particularly with James Gorman, the former Morgan Stanley CEO, as Disney’s chair.

Charan hailed Gorman as an unmatched strategist and evaluator of a portfolio of businesses, and D’Amaro as a leader who can bring a vision to life and nail every detail.

“It will be the reinventing of Disney,” Charan said. “You have the best expert as chairman and you now have a person who knows how to execute.”

Abel, Ternus, Furner, and D’Amaro follow a rich tradition of nuts-and-bolts CEOs, from General Electric’s Jack Welch to Tesla and SpaceX’s Elon Musk.

George recalled visiting Musk’s Tesla factory in California a few years back.

“Man, he understood all the nuts and bolts,” George said, adding that Musk combined his grasp of the nitty-gritty with unmatched vision and creativity.

“What he did at SpaceX is nuts and bolts,” George continued. “Can you imagine doing more than anyone at NASA with all those tens of billions of dollars coming in?”

George said that Abel, Ternus, Furner, and D’Amaro had to be nuts-and-bolts leaders to reach the top of their companies, but that’s only “part of the equation.”

To succeed as CEOs, George said, they’ll need a compelling 10-year vision for their companies, and a deep understanding of their industries and the wider business environment.

They must also have the courage to make big bets and transform their companies as required, and the ability to adapt rapidly in a fast-changing world, he added.

“He can’t just be a hardware guy,” George said about Ternus, while discussing how Apple’s AI strategy will be key in the years ahead. “If that’s all he does, he’ll fail.”

George also underscored the need fo D’Amaro to determine what to do with ESPN and Disney’s broader TV-and-cable business, which has faced a slew of challenges in the streaming era.

The leadership guru, who runs training courses for CEOs, emphasized that the step up to CEO only gets harder when you’re succeeding a legend and shouldering enormous expectations.

“How would you like to follow Warren Buffett?” George quipped. He also pointed to Iger’s transformative acquisitions, Cook’s vision and courage to break from Jobs and play to his strengths in supply-chain logistics, and Furner’s bold embrace of e-commerce at Walmart.

“These gentlemen have their work cut out for them,” he said.