Apple was co-founded by Steve Jobs, Steve Wozniak and Ronald Wayne. Steve Jobs liked to keep things simple, but apparently Ronald Wayne didn't. This is evident in the original Apple logo, designed by Ronald Wayne himself in 1976.
The first Apple logo is vastly different than the simplistic Apple logo we know today. It shows Isaac Newton sitting under an Apple tree, with an apple dangling above his head. The banner reads "Apple Computer Co." and on the outside border there's small text that says: "Newton... a mind forever voyaging through strange seas of thought... alone."
The original Apple logo didn't last long, because the very year Apple was founded it changed to the more familiar design of an Apple, albeit a rainbow colored apple. Steve Jobs commissioned graphic designer Rob Janoff to create a more modern logo and it stuck from '76 to '98. The Apple has a bite on it, which is a geeky play on words (bite/byte). Another reason the Apple has a bite on it was to make it clear that it's an apple and not a tomato or a cherry.
When Steve Jobs returned to Apple in 1997 he decided to change the logo once again. The Apple logo was one of the most recognized logos ever, but it wasn't that futuristic. Steve wanted to keep the design of the Apple logo, but having a big rainbow splashed on Apple products didn't look all that great. It was then that the Apple logo went black and it hasn't gone back. With the new logo change Apple could place their new logo, whether the black one or the monochrome one, as big as they wanted on their products.