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. John Ternus is just the third Apple CEO in 30 years. Key points and original sources are listed below.

• 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 lette...S1

• John Ternus is just the third Apple CEO in 30 years. His primary challenge is to correct the company's faltering AI strategy to preserve its position as a big tech leader.S2

• Also: All the news and watercooler chat from Fortune.S3