Sihon was an Amorite king of the city of Heshbon and its surrounding land. Along with Og, King of Bashan, Sihon was defeated by the Israelites, specifically for attacking Israel when requested to peacefully pass through their lands. While the description of the battle against Sihon is brief, Sihon is an important of Israel's national memory as an example of God's faithfulness to his promises (in like manner to The Exodus, though to a much lesser extent). Outside of his historical description in the Book of Numbers and recapitulation in Deuteronomy, Sihon is referenced in Joshua, Judges, Nehemiah, two psalms and Jeremiah.
King of Heshbon
Sihon, an Amorite, ruled over his own kingdom led by the city-state of Heshbon. Though Sihon was an Amorite, he ruled his own kingdom opposite Og; Amorite was an ethnic designation and not a constituted nation (as is the case for most people groups in those days). From his rule in Heshbon, Sihon exercised influence over many villages extending up to the Arnon River and Ammonite country. In a conflict with a king of Moab, Sihon defeated him and took all of his territory extending to the Arnon River. This lead him to obtaining great power and renown among the nations and thus made his defeat at the hands of the Israelites a clear act of God.