The definition of theophany is a visible manifestation of God found in the Old Testament. God had appeared as an angel, Genesis 16: 7-14 (NASB):
7 Now the angel of the LORD found her by a spring of water in the wilderness, by the spring on the way to Shur. 8 He said, “Hagar, Sarai’s maid, where have you come from and where are you going?” And she said, “I am fleeing from the presence of my mistress Sarai.” 9 Then the angel of the LORD said to her, “Return to your mistress, and submit yourself to her authority.” 10 Moreover, the angel of the LORD said to her, “I will greatly multiply your descendants so that they will be too many to count.” 11 The angel of the LORD said to her further,
“Behold, you are with child,
And you will bear a son;
And you shall call his name Ishmael,
Because the LORD has given heed to your affliction.
12 “He will be a wild donkey of a man,
His hand will be against everyone,
And everyone’s hand will be against him;
And he will live to the east of all his brothers.”
13 Then she called the name of the LORD who spoke to her, “You are a God who sees”; for she said, “Have I even remained alive here after seeing Him?” 14 Therefore the well was called Beer-lahai-roi; behold, it is between Kadesh and Bered.
Many scholars say that the above scripture has many similarities to add to a conclusion that the angel of the Lord is actually a manifestation of Jesus.
Also God had appeared in many visions and dreams; Genesis 15: 1-21, and in Isaiah 6: 1-13.