It is more commonly understood that this was the righteous Hezekiah, king of Judah (2 Kings 18:1 – 20:21; Isaiah 36:1 – 39:8). We cannot be certain, since we do not have the full genealogy of all the sons of Hezekiah, and the name Hezekiah
was a common personal name in the West Semitic context. Furthermore, it is noted that while Amon” is called king
in Zephaniah 1:1, Hezekiah is not.
But in all likelihood it is King Hezekiah. The absence of king
with Hezekiah’s name could be because Zephaniah’s contemporaries knew he was of royal blood. This royal genealogy would also explain the unusual move of tracing trace the genealogy of Zephaniah to the fourth generation. Dillard and Longman conclude that there can be little question
that Zephaniah’s royal lineage is the reason for the length of the genealogy.
If it is King Hezekiah, that would make Zephaniah of the royal line of Judah, as the great-great-grandson of King Hezekiah (ca. 715–686 BC). This link might clarify the prophet’s interest in the royal court (e.g., Zephaniah 1:8; Zephaniah 3:3–4) and his awareness of international affairs. Zephaniah only concerns himself with the ethics in the upper eschelons of society in Jerusalem—princes, judges, prophets, priests (Zephaniah 1:4, Zephaniah 1:8–9; Zephaniah 3:3–4)—and not really with the average Israelite.1 This link to King Hezekiah would also make him a distant cousin of Josiah, and possibly then a close ally, whose prophecies may have strongly impacted Josiah in the years leading up to his reforms.2
1 The word of the LORD that came to Zephaniah the son of Cushi, son of Gedaliah, son of Amariah, son of Hezekiah, in the days of Josiah the son of Amon, king of Judah.