Steve Jobs has resigned as Apple's leader. The move has been speculated because of questions over Jobs' health. He was diagnosed with a rare form of pancreatic cancer in 2004 and underwent a liver transplant two years ago.

Speculation has focused in recent months on when Jobs might retire, but even though the timing might come as a surprise, Jobs' impact as a 21st century leader is clear.

Here are five reasons Apple's Steve Jobs made his mark as one of the greatest CEO's the world has ever known:

1) He was anti-bureaucracy. Bureaucrats tried to run Jobs away from Apple, and did for a spell. But when the company was nearing failure as only a computer maker, Jobs came back onto the scene. So maybe he wasn't good at business, he effectively said. But I know the consumer! he said. And, he did.

Jobs single-handily reshaped Apple, launching the iPod and focusing on back office support and sales -- iTunes. The rest is history. A bureaucrat might have launched the iPad, which Apple designers showed him first before the iPhone, but instinct told Jobs consumers weren't ready yet.

So, Jobs pushed the iPhone first and years later he got a hit with the iPad tablet -- when the world was ready for it. Now, Apple is the global leader in smartphone sales of a single product. And, another single product.

Jobs is a genius at business because he was the antithesis of big business -- always. Oddly, though, that's exactly what he created -- one big global business.

2) Jobs knew the customer. HP might have benefited from a few cues from Jobs. That company has herked and jerked recently. One minute it is launching the TouchPad tablet to compete with Apple's iPad. The next, it is killing the TouchPad and apparently walking away from its webOS system.

Jobs built Apple by shaping the corporation as a tech company counterculture, following instincts based upon the customer. He felt customers wanted technology streamlined, and simple, so he brought them that very thing and he tied them all together.

The iPhone works with the Mac computer. The Mac computer workds with the iPod. The iPad works with the iPhone, etc. The trend in U.S. tech was just the opposite, but Jobs emulated consumer wants -- simple products, big delivery. He knew the customer, and delivered.

3) He did what he loved. For Jobs, the professional realm was also a passion. It's a lesson all of us can learn, if we haven't yet. He loved products, people and innovation -- and he tied the three together better than perhaps any corporate leader ever has. He loved his job, and he hired people who loved the very same thing, thus, he created great synergy at Apple. They love product, people and innovation, and it has worked very well in the broad scope.

4) He thought small, but executed big. VERY BIG. Steve Jobs wanted to put a ding in the universe. He once said that. And, he certainly did that as Apple's leader. But, he also thought very, very small.

For instance, he worried over the iPod's functionality, and he stressed over the iPhone's touchscreen ease. Small things kept him up at night, but big things kept him coming back to the office for more. In other words, Jobs dreamed big, but thought small. It's how he's taken the iPhone to more than 100 million global consumers in a matter of years.

The iPhone conquered the globe, but he thought small most every day about how Apple should make the product so that so many people would want it. Guess what? They do.

5) Innovate by learning from failures. Apple is known at the end of Jobs' leadership tenure as a company that can do no wrong. Why, just as Jobs announced his retirement the company has more than $76 billion in cash on the books and is the global smartphone and tablet leader. Laptop computer sales aren't too bad, either.

But Apple and Jobs misstepped plenty of times over the years. That's why he was once run out of the company's leadership role. But when he came back, Jobs was stronger in that role than ever before. He overcame fear by learning from his failures. That power unleashed the greatness that Apple ultimately became under Steve Jobs.