Satan occurs first - in 1 Chronicles 21. Satan is from the Hebrew meaning 'adversary' from the word meaning 'to plot against'.
In Isaiah 14, the king of Babylon sarcastically refers to Satan as 'the Light-Bearer' (Latin Lux or Luc 'light' + fer 'to bear') or the Day Star, (ie. the planet Venus which is visible in the morning sky) 'fallen from heaven' ie. fallen from power. To see how clear this is, it reads (I use the Basic English Bible - too impatiant with the others) "How great is your fall from heaven, O shining one, son of the morning! How are you cut down to the earth, low among the dead bodies!" - you can clearly see he was taking the mick ;o) In the Vulgate this was translated to "Quomodo cecidisti de caelo lucifer qui mane oriebaris corruisti in terram qui vulnerabas gentes" and voila, you get the basis of the concept of 'Lucifer' as a person.
That verse was partly quoted by Jesus in Luke 10:18 where he says "I was watching for Satan, falling from heaven like a star" so from the time of Jerome (core writer of the Vulgate, Roman with about 1 year of Hebrew study under his belt ;o) onwards Satan as Lucifer was an accepted concept.
As it was originally used, it was a reference not to a person at all, simply the phenomenon of Venus in the morning sky and a handy way to chide 'my how you've fallen'. Personally, I doubt seriously anyone saying Satan and Lucifer are two different demons has even read a Bible, let alone studied the many incarnations of it.