Lucifer was not the name of the king in Isaiah 14. As your linked Wikipedia article mentions, it's debated which king of Babylon is referenced in the passage. It names Nebuchadnezzar, Nabonidus, and several Assyrian kings as possibilities. So where does "Lucifer" come from?
So where did "Lucifer" come from? Let's look at Isaiah 14:12 in a literal English translation of the Hebrew:
How hast thou fallen from the heavens, O shining one, son of the dawn!
Thou hast been cut down to earth, O weakener of nations.
In the original Hebrew, "shining one" is הֵילֵל. When the Bible was translated into Latin, that was rendered "Lucifer." For some reason, the translators of the KJV carried that translation over as though it were a proper noun, when it simply means "shining one" or "morning star" literally, a possible reference to Venus.
So why have Christians applied the verse to Satan if it was about the king of Babylon? No one disputes that it is about the king of Babylon -- who is not named Lucifer -- but some believe that God's rebuke to the king of Babylon is identifying him allegorically with Satan. Not that he is Satan, but that as an evil one, he can be identified with Satan. They point out two New Testament verses (in Luke 10 and Revelation 12) speak of Satan "falling" from heaven. They also point out that verses 13 and 14 sound similar to the devil's words in Genesis 3: "You shall be as God."
Not all Christians believe Isaiah 14 refers to the devil in any capacity. John Calvin and Martin Luther both spoke out against that interpretation.
So to sum up:
Lucifer is not really a name to begin with.
It has nothing to do with cruelty.
People think Isaiah 14 has to do with Satan because of its talk of pride and of falling from heaven.
"Lucifer" is a Latin translation of a Hebrew word.