What did Gideon name the altar he built at Ophrah after seeing the angel?

Answer: The LORD Is Peace

Afraid after seeing the angel face to face, Gideon heard, "Peace be with you," and named the altar The LORD Is Peace (KJV: Jehovah-shalom).

“When Gideon realized that it was the angel of the LORD, he said, “Oh no, Lord GOD! I have seen the angel of the LORD face to face!””— Judges 6:22 (BSB)