Heidegger's Bible Handbook: Haggai: Author

1.  The author is חַגַּי/Haggai, which signifies festal.  He was a Prophet of great Spirit.

The preceding Prophets were before the Babylonian captivity:  the following three, Haggai, Zechariah, and Malachi, prophesied after that.  The first is חַגַּי, Haggai or Haggæus, which appears to denote joyful or festal; who he was is not evident.  Nevertheless, that he, together with Zechariah, was of great courage and Spirit, Jerome rightly argues from this, that against the edict of Artaxerxes, and the Samaritans, and all the nations round about, impeding the building of the Temple,[1] he did not fear to command that the Temple be constructed.

[1] See Ezra 4.