Who did John the Baptist clear the way for?

Isaiah 40:3 NWT

A voice of one calling out in the wilderness: ‘Clear up the way of Jehovah! Make a straight highway through the desert for our God.’

Who is the "one calling out in the wilderness" preparing the way for?
Mark 1:2-4 NWT

Just as it is written in Isaiah the prophet: “Look! I am sending my messenger ahead of you, who will prepare your way. A voice of one crying out in the wilderness: ‘Prepare the way of Jehovah, make his roads straight,’” John the Baptizer came baptizing in the wilderness and preaching baptism in symbol of repentance for forgiveness of sins.

Who is the one crying out in the wilderness?
Who is he preparing the way for?
Malachi 3:1 NWT

“Look! I am sending my messenger, and he will clear up a way before me. And suddenly the true Lord, whom you are seeking, will come to his temple; and the messenger of the covenant will come, in whom you take delight. Look! He will certainly come,” says Jehovah of armies.

Who is speaking?
Who is the messenger that he is sending?
Who will come to his temple? 
Who is the messenger of the covenant?
Who is the true Lord?
Luke 1:76 NWT

But as for you, young child, you will be called a prophet of the Most High, for you will go ahead of Jehovah to prepare his ways,

Who is the prophet of the Most High?
Who is the Jehovah that the prophet will go ahead of?