Who Killed the giant Goliath?

We read in 1 Samuel 17: "David killed Goliath" > And as he talked with them, behold, there came up the champion, the > Philistine of Gath, Goliath by name, out of the ranks of the > Philistines, and spake according to the same words: and David heard > them. **1 Samuel 17:23 ASV** (...) >Then David ran, and stood over the > Philistine, and took his sword, and drew it out of the sheath thereof, > and slew him, and cut off his head therewith. And when the Philistines > saw that their champion was dead, they fled. **1 Samuel 17:51 ASV** But we read in 2 Samuel 21: "Elhanan killed the giant Goliath" > And there was again war with the Philistines at Gob; and Elhanan the > son of Jaareoregim the Beth-lehemite slew Goliath the Gittite, the > staff of whose spear was like a weaver’s beam. **2 Samuel 21:19 ASV** So, who killed Goliath?