Steve Jobs, mastermind behind Apple, has resigned as CEO of the company effective immediately.

Tim Cook, formerly Apple, Inc’s chief operating officer, has been named the new CEO, Apple’s board of directors announced on Wednesday. Jobs has been appointed chairman of the board.

“I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple’s CEO, I would be the first to let you know,” Jobs wrote in a letter to Apple’s board on Thursday. “Unfortunately, that day has come.”

Jobs was diagnosed with a rare form of pancreatic cancer in 2004. In January of this year Jobs stepped aside to “focus on [his] health.” He has declined to elaborate on his condition.

Under Jobs, Apple delivered innovations from the first mouse-driven user interface to the pocketable iPod media player, which created the digital music revolution. It delivered the first popular tablet computer, the iPad, prompting a wholesale reinvention of the media business in the process. And as chief executive officer of Pixar Studios, Jobs became the tech-savvy equivalent of Walt Disney, fine-tuning the art of computer-generated storytelling beginning with Toy Story. Today, Apple continues to expand its reign in the mobile wireless industry with its phenomenally successful iPhone.