Read the Book of Enoch and you'll learn Azazel was the chief Watcher (angel assigned to look over humans), and led the original rebellion against God.

The ancient Israelites observed the Day of Atonement (Yom Kippur) each year, and there were 2 goats in the ceremony. In Leviticus 16, the elements of the ceremony are laid out, and casting lots to determine which goat belongs to God, and is sacrificed as a sin offering, and which goat is the scapegoat (all the sins of the people fall on said goat) and it is left alive and wanders into the wilderness alone.

Leviticus 16:6-10

6 And Aaron shall offer his bullock of the sin offering, which is for himself, and make an atonement for himself, and for his house.

7 And he shall take the two goats, and present them before the Lord at the door of the tabernacle of the congregation.

8 And Aaron shall cast lots upon the two goats; one lot for the Lord, and the other lot for the scapegoat.

9 And Aaron shall bring the goat upon which the Lord's lot fell, and offer him for a sin offering.

10 But the goat, on which the lot fell to be the scapegoat, shall be presented alive before the Lord, to make an atonement with him, and to let him go for a scapegoat into the wilderness.

Interestingly enough, the word translated as Scapegoat is Azazel.

From the Blue Letter Bible-

for a scapegoat

h5799 לַעֲזָאזֵל עֲזָאזֵל ʿăzā'zēl

https://www.blueletterbible.org/kjv/lev/16/10/p0/t_conc_106010