According to the Book of Judges, Eglon was king of Moab who oppressed Israel.
He was the head of the confederacy of Moab, Ammon and Amalek in their assault on Israel. Eglon reigned over the Israelites for 18 years. One day, Ehud, who was left handed, came presenting a customary tribute and tricked Eglon and stabbed him with his sword, but when Ehud attempted to draw the sword back out, the obese king's excess fat prevented its retrieval. His servants, believing he was relieving himself, left him be. In the aftermath of his death, the Moabites were routed and the Israelites enjoyed eighty years of peace.
Rabbis in the Talmudic tradition claimed that Ruth was Eglon's daughter. According to this tradition, Eglon was rewarded for rising out of respect when Ehud mentioned the Israelite God by having King David as a descendant. This can also be seen as an attempt to provide a royal lineage to David. The Talmud also describes Eglon as the grandson of Balak. There is, however, no basis in the actual verses for such an assertion.