What was Azaryhahu appointed over?
Radak, Malbim: The Navi does not tell us.
Metzudas David: Perhaps Shlomo made him the Mashu'ach Milchamah. Even though (Shmuel II, 20:26) David made Ira [Mashu'ach Milchamah] in place of Tzadok (who became Kohen Gadol), perhaps Ira died before he was appointed 1 .
Malbim citing Mahari: Also he was a scribe, together with Elichoref and Achiyah mentioned right after this.
Why does Metzudas David say so? Perhaps David appointed Ira, and after Ira died, Shlomo appointed Azaryhahu in place of him! The verse that Metzudas David cited said only that Ira was a Kohen to David; there, Metzudas David explained that perhaps he was an officer and counselor to David, or that David used to send all of his Matanos Kehunah to him! (PF)
Was Azaryhahu truly Tzadok's son?
Radak #1, Malbim: He was his grandson, for he was the son of Tzadok's son Achima'atz (Divrei ha'Yamim I, 5:34-35).
Radak #2: Perhaps he was, if this Tzadok is not Tzadok ben Achituv who was anointed to be Kohen Gadol when Shlomo was anointed (Divrei ha'Yamim I, 29:22).
