Which king of Aram besieged Samaria?

Answer: Ben-Hadad

Ben-Hadad king of Aram mustered his entire army and besieged Samaria.

“Now Ben-hadad king of Aram assembled his entire army. Accompanied by thirty-two kings with their horses and chariots, he marched up, besieged Samaria, and waged war against it.”— 1 Kings 20:1 (BSB)