Steve Jobs, the man credited with turning Apple into one of the most industry-shaping companies around, has resigned from his position as chief executive officer.

The 55 year old, who co-founded the technology giant from a garage, has been on medical leave for an undisclosed condition since January. He previously survived pancreatic cancer. In his resignation letter, Jobs 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.

In a statement, Apple said that Tim Cook, who has been running things in Jobs' absence, will take over as chief executive, while Jobs will move to the newly-created role of chairman.

The decision has sent shockwaves through the business world, with shares in Apple dropping by at least 5 per cent in overnight trading.

Perhaps more than any other current corporate leader, Jobs is closely identified with the success of his company. Seen as a visionary, Jobs' many admirers say that his talent lies in predicting what consumers want before they know they want it.

He ran Apple twice. The first time was from its creation in 1976 until he was ousted in 1985, and the second was 20 years later when he returned to rescue the floundering company. He successfully turned Apple round, releasing a series of iconic products. The iPod has reshaped the music industry, while the iPhone changed expectations of what a mobile phone should do.

Earlier this month, Apple briefly became the world's most valuable company, overtaking the oil giant Exxon Mobil, worth over $350bn. It didn't last long, but is astonishing given that Apple sells things that people want, rather than necessities like oil.

Over at the Telegraph, Shane Richmond suggests that it is important not to overstate the impact of Jobs' departure:

Apple's innovations over the last decade are the result of the company's structure: a small team at the top, focusing on a tightly-controlled number of products. Ideas can come from anywhere but those top executives spend a lot of time deciding what not to work on, to ensure that the company's resources aren't spread too thinly. Though Jobs played a key role in developing those working practices, the ideas are embedded deep within the company by this point. Apple's competitors might be hoping that the company's fortunes will change for the worse without Jobs but I wouldn't bet on it.

Whether Apple continues to hit the mark remains to be seen, but the technology industry has lost one of its most charismatic figures.