When the rain came at last, Elijah ran ahead of whom all the way to Jezreel?

Answer: King Ahab

As Ahab rode off to Jezreel, the hand of the LORD came on Elijah; he tucked his cloak into his belt and ran ahead of Ahab all the way.

“Meanwhile, the sky grew dark with clouds and wind, and a heavy rain began to fall. So Ahab rode away and went to Jezreel. And the hand of the LORD came upon Elijah, and he tucked his cloak into his belt and ran ahead of Ahab all the way to Jezreel.”— 1 Kings 18:45-46 (BSB)