Judges 13:17-20 (NKJV)
Then Manoah said to the Angel of the Lord , "What is Your name, that when Your words come to pass we may honor You?"
And the Angel of the Lord said to him, "Why do you ask My name, seeing it is wonderful?"
So Manoah took the young goat with the grain offering, and offered it upon the rock to the Lord. And He did a wondrous thing while Manoah and his wife looked on--it happened as the flame went up toward heaven from the altar--the Angel of the Lord ascended in the flame of the altar! When Manoah and his wife saw this, they fell on their faces to the ground.
Manoah was visited by the Angel of the Lord announcing the birth of Sampson. When the Old Testament speaks of the "Angel of the Lord" it is referring to a pre-incarnate appearance of Jesus Christ. The first clue here in this verse is that the Angel would not give His name seeing that it was beyond human ability to hear or understand. The final proof that this is the Lord Himself is the fact that the Angel of the Lord received the sacrifice and worship of Manoah and his wife. No mere angel would accept such worship.
Jesus is called Wonderful because he indeed deserves our astonishment and rapt attention.
Isaiah 9:6 (NKJV)
For unto us a Child is born, Unto us a Son is given; And the government will be upon His shoulder. And His name will be called Wonderful, Counselor, Mighty God, Everlasting Father, Prince of Peace.