Who is Isaiah talking about in chap. 14?
The Alexandrian school, with its love of allegory, identified Isa 14 with the fall of Satan ("Lucifer," Vulgate).
The Protestant Reformers rejected this identification, and they've been followed by a number of contemporary commentators. However:
i) It may well be true that the immediate historical referent is to some Mesopotamian king. Various candidates have been proposed, viz., Belshazzar, Nabondinus, Nebuchadnezzar, Sargon, Sennacherib, Tiglath-pileser.
The concrete referent depends, in part, on whether you favor the tradition or liberal late dating of the book. In addition, inspiration is not bounded by the past or present time-horizon.
We should also resist the temptation to draw too fine a distinction between king and kingdom (a whole dynasty).
ii) That, however, doesn't account for the imagery itself. There is, in comparative mythology, a revolt-in-heaven motif. This lies behind Isa 14.
One suggestion would be that Isaiah is making use of stock mythopoetic imagery, in the manner of Milton and Dante, in his taunt-song to whomever the historical referent happens to be.
iii) That, however, doesn't account for the origin of the motif. Since, in terms of genealogy, all of these cultures go back to a common point of origin (Gen 9-11), the common motif likely has its roots in a primordial tradition, of which Scripture either preserves the authentic tradition or corrects a corrupted version.
iv) The three-decker universe, with heaven as the abode of supernatural agents, terra firma as the abode of earthlings, and the netherworld as the realm of the dead seems to be a cultural universal. It's a natural figurative extension of an earthbound observer's viewpoint.
v) The analogy between stars and angels is commonplace in Scripture.
vi) Again, by logical extension, is the analogy between waning/falling stars (e.g., meteors) and fallen angels. (v)-(vi) figure in Revelation. See also Lk 10:18 (cf. Isa 14:12, LXX).
vi) Since (the planet) Venus is the brightest star in the night sky, and since it has its own periodic phases (the transit of Venus), causing it to wax and wane, it is a natural choice to illustrate a fall from heaven.
vii) In apocalyptic literature, you have a micro/macroscopic parallel between earth and heaven. For example, pagan kingdoms are treated as front-organizations for the invisible kingdom of darkness--working behind-the-scenes.