Which Amorite king refused Israel passage and was defeated by Israel at Jahaz?

Answer: Sihon

Sihon gathered his army against Israel at Jahaz; Israel put him to the sword and took his land from the Arnon to the Jabbok.

“But Sihon would not let Israel pass through his territory. Instead, he gathered his whole army and went out to confront Israel in the wilderness. When he came to Jahaz, he fought against Israel.”— Numbers 21:23 (BSB)