The ongoing Apple versus Google war can be traced back to Google's entry into the smartphone market. Apple launched its iPhone in the Summer of 2007, and within two years Google answered back by releasing its mobile OS, Android.
This led to a series of events, and eventually an onslaught of litigation between the two companies over "copycatting." The jury is still out on who copied who, but Daring Fireball points to some evidence that seemingly falls in Apple's favor...