Tim Cook will step down as chief executive of Apple on September 1, ending a 15 year tenure that transformed the company into one valued at more than 4 trillion dollars. He will assume the role of active chair of the board, while John Ternus, currently the company’s senior vice president of hardware engineering, will take over leadership after a structured transition this summer.

Cook took the helm in 2011 following the death of founder Steve Jobs, at a time when many doubted the company’s future. Under his leadership, Apple expanded its product lineup beyond the iPhone and iPad with devices such as AirPods, Apple Watch, and Vision Pro, while also building a powerful services business that drove sustained financial growth.

Despite record-breaking market value, Cook faced criticism from some who believed the company had lost some of its earlier design boldness. Ternus, a longtime hardware leader who joined Apple in 2001, is closely associated with product development and recently played a key role in launching the MacBook Neo, a lower priced laptop aimed at broadening the company’s reach.

In a farewell letter, Cook praised Ternus as a brilliant engineer and thoughtful leader, expressing confidence in his successor’s ability to guide the company forward. Investors and analysts will now watch closely to see whether a hardware focused chief executive can usher in a new chapter of innovation at the technology giant.