Hasun ben Mashiach was a Karaite scholar who flourished in Egypt (or Babylonia) in the first half of the tenth century.
According to Steinschneider, "Hasun" is a corrupted form of the Arabic name "Hussain," the ו being easily confounded in manuscript with the י Hasun, or, as he is generally quoted by the Karaite authorities, ben Mashiah, was a younger contemporary of Saadia Gaon, whom, according to Sahl ben Matzliah in his Tokahat Megullah, he once challenged to a religious controversy.
Owing to a misunderstanding of a passage (§ 258) in the Eshkol ha-Kofer of Hadassi, Ḥasun was erroneously credited with the authorship of the anonymous chapter on theodicy, entitled Sha'ar Tzedek (St. Petersburg, Firkovich MSS.
Simḥah Isaac Luzki attributes to Ḥasun also a work on the precepts (Sefer ha-Mitzvot).
Abraham ibn Ezra, in his introduction to the commentary on the Pentateuch, quotes a Karaite scholar named Ben Mashiah, who is probably identical with Hasun.