Who Really Killed Goliath?

In chapter 21 in the Book of Samuel, we read, “…and Elhanan the son of Jaare-oregim the Beth-lehemite slew Goliath the Gittite.”  Um... didn’t we read earlier that David slew Goliath?  One possibility: David was a royal name he took up upon assuming the monarchy, and Elchanan was his name previously (we see no references to David by name prior to his beginning on his royal track.)  Another possibility is that the giant David killed in his youth was not Goliath.  Once the back-and-forth between David and the giant ensues in Samuel I 1:17, the giant is always referred to merely as, “the Phillsitine,” or, “the uncircumcised one.”