Although OS X is now an integral part of the Mac experience, it represented a big gamble for Apple when the first general release version — code-named Cheetah — arrived on March 24, 2001. It was also a gamble that Apple had little choice in making — and one that has paid off in the 15 years since, becoming, directly and indirectly, one of the critical factors in Apple’s success.

Still, there were many points at which things could have gone awry and decimated the company.

[For a more visual timeline of OS X, check out our slideshow, The evolution of Mac OS X.]

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