In Isaiah 44:6, the LORD says, "I am the first and I am the…"

Answer: Last

The LORD of Hosts, Israel's King and Redeemer, declares, "I am the first and I am the last, and there is no God but Me."

“Thus says the LORD, the King and Redeemer of Israel, the LORD of Hosts: “I am the first and I am the last, and there is no God but Me.”— Isaiah 44:6 (BSB)