Isaiah 1:1
חֲזוֹן יְשַׁעְיָהוּ בֶן אָמוֹץ אֲשֶׁר חָזָה עַל יְהוּדָה וִירוּשָׁלִָם בִּימֵי עֻזִּיָּהוּ יוֹתָם אָחָז יְחִזְקִיָּהוּ מַלְכֵי יְהוּדָה
The vision of Isaiah, son of Amotz, that he saw regarding Judah and Jerusalem in the days of Uziyahu, Yosam, Achaz, and Chizkiyahu, kings of Judah.
The Talmud (Megillah 10b) tells us that Isaiah’s father, Amotz, was the brother of King Amatziah. This made Isaiah first cousins with Uziyahu, who was king when Isaiah became a prophet. The ibn Ezra explains that this is why Isaiah was not subject to the constant persecutions that Jeremiah suffered: he was protected as a member of the royal family.