One of the best examples of a leader’s departure having a big impact on a company is likely Apple (AAPL). One of the founding forces of the company, Steve Jobs is virtually synonymous with the company he leads. That wasn’t the case in 1985, however, when he was forced out of the company because of disagreements with the CEO about the direction of the computer maker (Jobs was Chairman of the Board at the time). Apple floundered badly after Jobs’ departure. Eventually the company bought Jobs’ new company, called NeXT, to get him back in the corner office at Apple. The performance of the company (and it’s stock) since has been nothing short of dramatic, including the launch of the iPod, iPhone, iPad, and the iTunes media store.

Clearly Jobs’ vision plays a vital role in Apple’s success. Having him back at the helm is important to both the performance of the company and its shares, as investors are well aware of how vital his vision is to the company’s future. This why there was such concern in early 2009 when Jobs took a medical leave of absence to deal with pancreatic cancer.

Such medical concerns have surfaced several times in recent years and, while not appearing to have impacted the company’s performance over the longer term, each time the medical condition has surfaced in the media it has temporarily impacted Apple’s stock price in a negative way. Jobs’ announcement on January 17, 2011 that he is taking another leave of absence sent Apple shares materially lower overseas (U.S. markets were closed for the Martin Luther King Jr. Holiday on the day of the announcement).

Although all wish Steve Jobs the best in whatever medical issue he is dealing with, his health is a material issue about which shareholders should be aware. What are the plans if and when he does not return? Is there anyone who can provide the vision he has provided the company? Is Apple the same company without Steve Jobs? If these questions aren’t on the minds of Apple investors, they should be.

There are other companies that have strong leaders who have left only to return when the company they once drove began to flounder. The list includes such well-known brands as Dell (DELL) and Starbucks (SBUX). However, there are a number of other companies where charismatic (or not so charismatic, depending on one’s view) leaders are a driving force.

Berkshire Hathaway’s (BRKB) Warren Buffett, for example, is also viewed as synonymous with the company he leads with Charlie Munger. Both men are beyond the age where retirement is the norm and illness leading to death is not considered rare or surprising. The company has a succession plan, though little is disclosed about it. Investors who own shares of Berkshire need to be cognizant of and comfortable with the succession issue at this company or they risk a nasty surprise when Buffet and/or Munger are no longer with the corporation.

Larry Ellison of Oracle (ORCL) is another example. While many criticize Ellison’s management style, he is clearly the driving force of the company he co-founded. The loss of Ellison, who is also at retirement age, could materially alter the technology company. Shareholders need to be aware of just how important this one man is to the future of the company and the price of the stock they hold.

Sumner Redstone of Viacom (VIA) is yet another leader who’s loss could materially alter both the company he leads and its shares. Often noted as one of the most powerful media magnates, his vision is a major driving force at Viacom. He is now well into his eighties. The company is clearly large enough to survive his departure, but the loss of his vision and leadership (which, like Ellison’s, is often criticized) could change Viacom’s appeal as an investment.

There are clearly many more companies with charismatic and influential leaders, such as John Chambers of Cisco (CSCO - Free Value Line Analyst Report). While most companies do indeed have “lives” of their own, their driving forces are still the people working within them. To ignore this fact is a mistake. These few examples highlight how vital it is for investors to keep this issue in mind when buying shares in a company and act as a warning for shareholders who own the companies at which Jobs, Buffett, Ellison, and Redstone work.

At the time of this article's writing, the author did not have positions in any of the companies mentioned.