SAN FRANCISCO – The man in the black shirt and jeans who knew people would fall in love with the iPod, iPhone and iPad before they did is stepping back from Apple Inc., which grew into one of the world’s strongest companies as its leader’s health failed him. Steve Jobs’ resignation Wednesday appears to be the result of an unspecified medical condition for which he took a leave from his post in January. Apple’s chief operating officer, Tim Cook, was quickly named CEO of the company Jobs, 56, co-founded in his garage 35 years ago.