
At the time Ezekiel was written, Israel was in apostacy again and if I'm not 
mistaken, Tyre was about to make war on Israel.  Like I said, the Prince of 
Tyre was the human ruler of Tyre.  He was a wicked man.  By calling Satan 
the King of Tyre, Ezekiel was saying that Satan is the real ruler over Tyre.

Don't think my interpretation is neccessarily the orthodox Christian one, 
although most Christian Bible commentaries interpret the King of Tyre as 
being a reference to Satan. (I haven't read Ezekiel throughly in a long 
time.)