Apple's chief technology officer, Avadis 'Avie' Tevanian, has announced that he will retire at the end of March. 

Tevanian joined Apple in 1997 from NeXT, the company Steve Jobs set up after his temporary departure from Apple in 1985. 

He started out as Apple's vice president of software engineering before becoming chief software technology officer in 2003. Tevanian is best known for his development work on Apple's Mac OS X operating system. 

Apple has not made an official statement on Tevanian's departure, except to say that he is leaving to pursue "other interests".

His departure comes as Apple reaches a number of milestones. The company celebrates its 30th birthday on 1 April, OS X racked up its fifth year last week, and Apple's iTunes music store sold its billionth song last month.