Life at Apple without Jobs may be more than just a hypothetical. The 53-year-old Silicon Valley pioneer had a malignant tumor removed from his pancreas four years ago. With fresh concerns about his health following his gaunt appearance at the World Wide Developers Conference two weeks ago, it’s fair to ask: who’s on that executive team — and which ones have a shot at ruling Apple once Jobs leaves (even if he exits years from now and not for health reasons)?

There are 11 men in all — not counting Jobs. A handful are familiar faces to the small community of professional Apple watchers. As far as the general public is concerned, they are invisible, hidden in the long shadow cast by Apple’s (AAPL) high-profile CEO.

Some seem more qualified to step into Jobs’ shoes than others, but judge for yourself. Here they are, as listed on the company’s Executive Profiles web page, in rough order of their chances of succeeding Steve Jobs.

Timothy D. Cook: Chief operating officer. A 12-year veteran of IBM (IBM) and Compaq, Cook, 47, probably has more direct line responsibility that anyone in the company — even Jobs. Not only is he head of the resurgent Mac division, but he’s responsible, as his official bio puts it, “for all of the company’s worldwide sales and operations, including end-to-end management of Apple’s supply chain, sales activities, and service and support in all markets and countries.” Cook’s deep knowledge of Apple’s operations and ready command of detail has won him the respect of the board of directors and the investment community. A bachelor with a passion for cycling, he’s as steady and low-key as Jobs is temperamental. A Wall Street Journal profile described Cook’s dressing down of another man at a meeting as so “professional and surgical” it was only afterward that observers realized the man had just had his head handed to him. Although some wonder whether Cook has enough charisma to run Apple, when the CEO was out of commission, Cook was the executive Jobs put in charge.

Tony Fadell. Senior vice president, iPod division. With his American swagger and his hair bleached white, Fadell, 38, stood out at button-down Philips Electronics (PHG), where he led an in-house pirate operation designing Windows CE-based devices. It was there that he came up with the idea of marrying a Napster-like music store with a hard drive-based MP3 player. He shopped the concept around the Valley before Apple’s Jon Rubenstein snapped it up and put Fadell in charge of the engineering team that built the first iPod. Ambitious and charismatic (and no longer a bleached blond), he now runs the hardware division that makes two of Apple’s three key product lines: the iPod and the iPhone.

Ron Johnson. Senior vice president, retail. Johnson, 49, was a retailing star at Target (TGT) before he came to Apple in 2000, and he’s an even bigger star today, having designed what is arguably the world’s most user-friendly chain of retail stores. He shares Jobs’ single-minded focus on the customer experience, and when he parts ways with Jobs — the Genius Bar, where customers get hands-on troubleshooting, was a Johnson idea that Jobs resisted — he is often right. Most retailers focus on how you find the right item, he says, how you select it and how you get it out of the store. “We said there’s a bigger idea. Let’s design it around the customer’s life, not the moment when they’re in the store.” (link) Apple’s second-most charismatic public speaker, he is on several outsiders’ short list of possible successors.

Philip W. Schiller: Senior vice president, worldwide product marketing. An avuncular, unthreatening presence, Schiller, 47, plays a slightly rotund Sancho Panza to Jobs’ Quixote at nearly every Apple event. His deer-in-the-headlight performance — caught on videotape — when ambushed by a British TV reporter at the London unveiling of the iPhone contributed to the sense that Apple would be in trouble if Jobs were ever to leave. But it would be a mistake to underestimate Schiller. He has 24 years of marketing experience — 17 of them at Apple — and his official bio credits him with delivering a long list of “breakthrough” products: iMac, MacBook, Airport, Xserve, Mac OS X, Safari, AppleTV, iPod and iPhone.

Scott Forstall. Senior vice president, iPhone software. A veteran of NeXT, where he helped build the operating system that became OS X, Forstall came to Apple with Jobs in 1997. After proving himself by managing the team that released OS X Leopard, he was put in charge of software for the iPhone. “I actually have a photographer’s loupe that I use to make sure every pixel is right,” he told
Time
. “We will argue over literally a single pixel.” His profile was raised by public appearances at WWDC 2006 and the March ’08 SDK announcement. In an executive shakeup three days before WWDC 2008, he was elevated to senior vice president, reporting directly to Jobs. “Forstall is the man if SJ gets to pick [his successor],” says 9to5Mac‘s Cleve Nettles.

Jonathan Ive. Senior vice president, industrial design. Although his name is often floated as the next Apple CEO — and despite the fact that he garnered 49% of the votes in a recent online poll that asked “who would you trust to run Apple, without Jobs?” — Ive, 41, is probably the least likely of the leading contenders to take the job. Modest and notoriously shy (when he won the 2005 Design and Art Direction award it was Jobs who made the acceptance speech, although Ive was in the audience), he guards his privacy jealously; even Apple’s HR department doesn’t know exactly when he was born. Ive is perhaps the most influential industrial designer of our age. Why would he give up a job he clearly loves to take on the responsibilities of a CEO?

Below the fold: The also-rans.

Peter Oppenheimer. Chief financial officer. A long-time Apple senior exec — he joined he company in 1996 after a six years at Coopers & Lybrand and a sojourn at ADP (ADP), where he was CFO of the claims services division — Oppenheimer, 45, has the job formerly held by Fred Anderson (the ex-Apple CFO thrown under the bus in the options backdating scandal). Oppenheimer’s is a familiar voice to analysts and tech journalists. He turns up every three months on the company’s quarterly earnings call to rattle off Apple’s sales and revenue numbers and to offer his traditionally conservative guidance for the coming quarter. He took a lot of heat from shareholders in January when guidance even more pessimistic than usual sent the stock into a one-day 16-point nosedive.

Bertrand Serlet. Senior vice president, software engineering. One of only two members of Apple’s executive team for whom English is a second language — Fake Steve Jobs calls him a “friendly cyborg” from another planet, but he’s actually from France — Serlet, 47, came to Apple from Xerox PARC and NeXT, where he developed the workspace manager in NEXTSTEP and OPENSTEP. Having help port the NeXT operating system to Mac OS X, he took over Avie Tevanian’s software engineering post in 2003. Serlet is credited with leading development of 10.4 and 10.5 versions of OS X, but he’s most famous among Apple fans for his “Redmond, start your copiers” performance at WWDC 2006 — available on YouTube — pointing out similarities between OS X and Windows Vista.

Sina Tamaddon. Senior vice president, applications. Another non-native born American  (he’s Iranian), and yet another veteran of NeXT, Tamaddon, 50, came to Apple with Jobs’ return in September 1997. Although he’s held several top positions at Apple — including vice president and general manager of the Newton Group — and reports directly to Jobs, Tamaddon probably has a lower profile than anybody else on the executive team. He’s the only member without a bio on Apple’s official web page, and as this went to press, the question “Where did Sina Tamaddon go to school” had still not elicited any replies on WikiAnswers.

Daniel Cooperman. Senior vice president, general counsel and secretary. A relative newcomer, Cooperman, 56, joined Apple in November 2007 as the last move in a series of legal musical chairs (he left Oracle (ORCL) for Apple as Donald Rosenburg was leaving Apple for Qualcomm; Rosenberg had replaced Nancy Heinen, who is fighting SEC charges in the backdating case). Jobs began recruiting Cooperman last August after getting the okay from his friend Larry Ellison, according to Law.com, sweetening the pot with restricted stock worth $25 million. “The switcheroo was Larry’s idea,” wrote Fake Steve Jobs last September, when the move was announced. “Now that the feds are circling again he says I need some bad-ass mofo leading my team, not some namby-pamby Valley type. ‘I want you to have my consigliere,’ he told me. ‘He’s a good man. He can be trusted. Listen to him.'”

Bob Mansfield. Senior vice president, Mac hardware engineering. Mansfield has an important job: he heads the team that has delivered “dozens of breakthrough products,” according to his official bio, from the iMac to the Macbook Air. But he didn’t actually head the team when most of those breakthroughs were made. After stints at two companies specializing in 3D graphics chips, SGI and Raycer Graphics, he came to Cupertino in 1999 when Apple acquired Raycer. He was part of the troika that took over Mac engineering after the messy dismissal of Tim Bucher in 2004 and was formally put in charge of the division only last month. Unlike most senior VPs at Apple, he answers to Tim Cook, not Steve Jobs.