Sihon was an Amorite king of the region east of the Jordan River in modern-day Jordan with Heshbon as the capital of his kingdom.
He was defeated by Moses and the Israelites after the Exodus from Egypt. Other towns of Sihon's kingdom were: Aroer, Dibon, Jazer and Penuel.
Numbers 21:2-31:
21. Israel sent messengers to say to Sihon king of the Amorites:
22. "Let us pass through your country. We will not turn aside into any field or vineyard, or drink water from any well. We will travel along the king's highway until we have passed through your territory."
23. But Sihon would not let Israel pass through his territory. He mustered his entire army and marched out into the desert against Israel. When he reached Jahaz, he fought with Israel.
24. Israel, however, put him to the sword and took over his land from the Arnon to the Jabbok, but only as far as the Ammonites, because their border was fortified.
25. Israel captured all the cities of the Amorites and occupied them, including Heshbon and all its surrounding settlements.
26. Heshbon was the city of Sihon king of the Amorites, who had fought against the former king of Moab and had taken from him all his land as far as the Arnon.
27. That is why the poets say: "Come to Heshbon and let it be rebuilt; let Sihon's city be restored.
28. "Fire went out from Heshbon, a blaze from the city of Sihon. It consumed Ar of Moab, the citizens of Arnon's heights.
29. Woe to you, O Moab! You are destroyed, O people of Chemosh! He has given up his sons as fugitives and his daughters as captives to Sihon king of the Amorites.
30. "But we have overthrown them; Heshbon is destroyed all the way to Dibon. We have demolished them as far as Nophah, which extends to Medeba."
31. So Israel settled in the land of the Amorites.
Numbers 32:33:
33. Then Moses gave to the Gadites, the Reubenites and the half-tribe of Manasseh son of Joseph the kingdom of Sihon king of the Amorites and the kingdom of Og king of Bashan--the whole land with its cities and the territory around them.
Deuteronomy 1:4 mentioned King Sihon before he denied the Israelites safe passage through his lands in Deuteronomy 2:24-30:
24. "Set out now and cross the Arnon Gorge. See, I have given into your hand Sihon the Amorite, king of Heshbon, and his country. Begin to take possession of it and engage him in battle.
25. This very day I will begin to put the terror and fear of you on all the nations under heaven. They will hear reports of you and will tremble and be in anguish because of you."
26. From the desert of Kedemoth I sent messengers to Sihon king of Heshbon offering peace and saying,
27. "Let us pass through your country. We will stay on the main road; we will not turn aside to the right or to the left.
28. Sell us food to eat and water to drink for their price in silver. Only let us pass through on foot--
29. as the descendants of Esau, who live in Seir, and the Moabites, who live in Ar, did for us--until we cross the Jordan into the land the LORD our God is giving us."
30. But Sihon king of Heshbon refused to let us pass through. For the LORD your God had made his spirit stubborn and his heart obstinate in order to give him into your hands, as he has now done.
Joshua 12:1-6:
1. These are the kings of the land whom the Israelites had defeated and whose territory they took over east of the Jordan, from the Arnon Gorge to Mount Hermon, including all the eastern side of the Arabah:
2. Sihon king of the Amorites, who reigned in Heshbon. He ruled from Aroer on the rim of the Arnon Gorge--from the middle of the gorge--to the Jabbok River, which is the border of the Ammonites. This included half of Gilead.
3. He also ruled over the eastern Arabah from the Sea of Kinnereth to the Sea of the Arabah (the Salt Sea), to Beth Jeshimoth, and then southward below the slopes of Pisgah.
4. And the territory of Og king of Bashan, one of the last of the Rephaites, who reigned in Ashtaroth and Edrei.
5. He ruled over Mount Hermon, Salecah, all of Bashan to the border of the people of Geshur and Maacah, and half of Gilead to the border of Sihon king of Heshbon.
6. Moses, the servant of the LORD, and the Israelites conquered them. And Moses the servant of the LORD gave their land to the Reubenites, the Gadites and the half-tribe of Manasseh to be their possession.
Judges 11:19-22,26:
19. "Then Israel sent messengers to Sihon king of the Amorites, who ruled in Heshbon, and said to him, `Let us pass through your country to our own place.'
20. Sihon, however, did not trust Israel to pass through his territory. He mustered all his men and encamped at Jahaz and fought with Israel.
21. "Then the LORD, the God of Israel, gave Sihon and all his men into Israel's hands, and they defeated them. Israel took over all the land of the Amorites who lived in that country,
22. capturing all of it from the Arnon to the Jabbok and from the desert to the Jordan.
...
26. For three hundred years Israel occupied Heshbon, Aroer, the surrounding settlements and all the towns along the Arnon. Why didn't you retake them during that time?
Other minor references: Deuteronomy 3:2-6, 4:46, 29:7 and 31:4; Joshua 13:10-27; 1 Kings 4:19; Psalms 135:11 and 136:19; Nehemiah 9:22.
