Are there any people in the Bible that were half man and half eagle? Who is Nahum?
No, there were no people in the Bible who were half man and half eagle. But there is a special order of angels, called Cherubim (Ezekiel 1:4-14; 10:15-20), who look like a man and an eagle (on one side). These are unusual angels. Their description is awesome.
As for the form of their faces, each had the face of a man, all four had the face of a lion on the right and the face of a bull on the left, and all four had the face of an eagle. Such were their faces. Their wings were spread out above; each had two touching another being, and two covering their bodies. And each went straight forward; wherever the spirit was about to go, they would go, without turning as they went. In the midst of the living beings there was something that looked like burning coals of fire, like torches darting back and forth among the living beings. The fire was bright, and lightning was flashing from the fire. And the living beings ran to and fro like bolts of lightning. (NASB) Ezekiel 1:10-14
Nahum was a prophet of God who wrote the book of Nahum (it comes after the books of Jonah and then Micah). We know almost nothing about the prophet.
. . . The book of the vision of Nahum the Elkoshite. (NASB) Nahum 1:1
This passage tells us all that we know about him. He came from Elkosh which may have been part of Capernaum. His message was against Nineveh.
God does not always tell us everything we want to know. But He does tell us what we need for salvation.