For the first time since 2011, one of the world’s most valuable companies has a new leader, as today marks John Ternus’ first day as Apple’s CEO. He’s replacing Tim Cook, who will continue on as the executive chairman on Apple’s board and departed with a letter to employees that remarked, “This place is proof that culture triumphs over everything. We share a belief that what we build matters, and that we have both the opportunity and the responsibility to leave the world better than we found it.”

Ternus is taking over a company dealing with the rise of AI, shortages of RAM and other components due to that growth in AI, and a political and economic situation that is only getting more complicated as time passes. He will also do it without many of the executives who worked with Cook and Steve Jobs, like Phil Schiller, who Bloomberg reported will step down from his role leading the App Store.