It’s fairly rare to hear about a longtime Apple executive leaving their post -- especially one who’s stuck by the company's CEO for over two decades. Apple’s senior vice president of Mac Software Engineering is doing just that.

Apple announced on Wednesday that longtime senior vice president of Mac Software Engineering Bertrand Serlet is leaving Cupertino after 22 years. Craig Federighi will shift into his place from vice president of Mac Software Engineering, reporting directly to CEO Steve Jobs.

“I’ve worked with Steve for 22 years and have had an incredible time developing products at both NeXT and Apple, but at this point, I want to focus less on products and more on science,” said Apple’s senior vice president of Software Engineering, Bertrand Serlet. “Craig has done a great job managing the Mac OS team for the past two years, Lion is a great release and the transition should be seamless.”

Serlet spent four years at Xerox PARC prior to joining Steve Jobs’ NeXT in 1989 while the CEO was in exile from Apple. When Jobs returned to Apple in 1997, Serlet came along for the ride and was instrumental in developing Mac OS X. Apple notes that Serlet holds a doctorate in Computer Science from the University of Orsay, France.

His replacement, Craig Federighi, also worked at NeXT before Apple, but left for a decade as vice president of Internet Services and chief technology officer for Ariba prior to returning to Apple in 2009 to lead the Mac OS X engineering team. Federighi holds a Master of Science degree in Computer Science and a Bachelor of Science in Electrical Engineering and Computer Science from the University of California, Berkeley.

While it may be the end of an era for Serlet, Mac OS X certainly isn’t going anywhere, with 10.7 Lion headed our way this summer, bringing with it a bit of iOS to the desktop.

Check out Bertrand talking about Vista. Hilarious.

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(Image courtesy of Life.com)