Who rescued Jeremiah from the muddy cistern?

Answer: Ebed-melech

Ebed-melech the Cushite, a palace official, pleaded with the king and, with thirty men, pulled Jeremiah up with ropes.

“Now Ebed-melech the Cushite, a court official in the royal palace, heard that Jeremiah had been put into the cistern. While the king was sitting at the Gate of Benjamin,”— Jeremiah 38:7 (BSB)