Apple CEO Steve Jobs, who oversaw the company become ubiquitous to music fans with its invention of iTunes and the iPod has tendered his resignation as CEO of the company.

In a letter to the board announcing that he was quitting, he said “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. Unfortunately, that day has come.”

Jobs has been on medical leave since January, but is still expected to retain his position as Chairman. In his resignation letter he also said “I believe Apple’s brightest and most innovative days are ahead of it. And I look forward to watching and contributing to its success in a new role. I have made some of the best friends of my life at Apple, and I thank you all for the many years of being able to work alongside you.”

Jobs has handed over the day to day running of Apply to Chief Operating Officer Tim Cook, who has had the innate ability to receive approval from the notoriously hard to please Apple boss. Cook took up the post of COO in 2005, having “been doing this job for over two years,” according to Jobs at the time.

Cook has overseen much of the recent strategic growth of Apple since Jobs was diagnosed with pancreatic cancer which led to him receiving a liver transplant. His dramatic weight loss in recent years and enforced medical leave from Apple has led to suggestions that the cancer has returned and he has simultaneously been fighting the disease while running Apple.

iTunes Store is the largest music retailer in the US and has sold over 10 Billion songs worldwide since it opened in 2003.