Satan is called the "father of the lie" because he told the very first lie to Eve.
In the beginning, God told Adam to go nuts and eat all the fruit except the fruit from the tree in the middle of the garden. He said "but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall die."
So then fast forward, Eve was created and she's hanging out by the tree, talking to the serpent (Satan) and Satan says: "You will not die. For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil."
So what happened? They ate the fruit and died? NO. The Bible says they ate the fruit and suddenly their eyes were opened, they knew that they were naked, they knew good and evil that was previously hidden from them and they lived on for hundreds of years.
And by the way, since they didn't know good and evil before they ate the fruit, then how were they supposed to know that listening to God was good and listening to the Serpent and eating the fruit was evil? Either way, God got really pissed (like He usually does in the old testament) and cursed everybody, Adam , Eve, the Serpent, the ground, everything in sight, and then Satan gets the bad rap.
But how was Satan wrong and God proven true? Wasn't it the other way around? I mean, the name of the frickin' tree was "the tree of the knowledge of good and evil". Would it not make sense to Adam and Eve that its name pretty much gives away what it does? Otherwise it would be called "the tree of if you eat from it you'll be dead in 24 hours"? In my book, Satan wins this one.