"Hello," Apple's new chief executive John Ternus wrote on X on Tuesday, marking his debut on the social media site and his first public statement as CEO. Responses to the one-word post were overwhelmingly positive, and by Friday, Ternus had gained almost 1mn followers. The laconic message fits the 51-year-old hardware engineer and Apple veteran who reached the pinnacle of corporate America without building a large external profile.

"It was very obvious from the earliest days that John was super-talented," says Wendell Weeks, chief executive of longtime Apple glass supplier Corning. Weeks describes Ternus as a humble "good guy" and notes his car-racing hobby reveals another side. "You have to be wicked calm and really dedicated to excellence if you're good at it. And John is good at it."

Those reserves of calm will be of use as Ternus ends Tim Cook's 15-year reign. Apple is now a $4.7tn company whose supply chain sits at the centre of geopolitical tension. The share price is up 18 per cent this year, but product sales growth has slowed and investors want exciting new devices. Given the scale and complexity, "Apple today is just a different beast," says Wamsi Mohan, senior analyst at Bank of America.

Ternus is the first product engineer to lead Apple, with a 25-year career at the company. He belongs to the generation mentored by co-founder Steve Jobs. Cook will remain as executive chair, and the four-month transition has involved Ternus quietly accompanying him to public appearances, including Berkshire Hathaway's annual meeting. He studied mechanical engineering at the University of Pennsylvania, graduating in 1997 (the same year as Elon Musk), and joined Apple's product team in 2001.