Who answered God's call in the night: 'Speak, for Your servant is listening'?

Answer: Samuel

Told by Eli what to say, young Samuel answered the LORD's call: "Speak, for Your servant is listening."

““Go and lie down,” he said to Samuel, “and if He calls you, say, ‘Speak, LORD, for Your servant is listening.’” So Samuel went and lay down in his place. Then the LORD came and stood there, calling as before, “Samuel! Samuel!” And Samuel answered, “Speak, for Your servant is listening.””— 1 Samuel 3:9-10 (BSB)