From whom did King Omri buy the hill of Samaria?

Answer: Shemer

Omri bought the hill from Shemer for two talents of silver and named the city Samaria after him.

“He bought the hill of Samaria from Shemer for two talents of silver and built a city there, calling it Samaria after the name of Shemer, who had owned the hill.”— 1 Kings 16:24 (BSB)