Ezra 4:9 (ESV)

9 Rehum the commander, Shimshai the scribe, and the rest of their associates, the judges, the governors, the officials, the Persians, the men of Erech, the Babylonians, the men of Susa, that is, the Elamites,

Rehum was a high-ranking administrative official. He may1 or may not2 have been the governor, and is likely to have been resident in Samaria. Rehum is the shortened form of a Babylonian name Rahim-ili, my god is merciful, or Rahim-sarri, my lord is merciful.