After the high priest put on his robe, he put on his ephod. This was an apron-like garment.
Ex 28:
Who wore the ephod?
Exodus 28:
Samuel wore a plain linen ephod, 1 Samuel 2:

Ex 28:
Only the ruling high priest wore complete outfits with the golden ephod.6“Make the ephod of gold, and of blue, purple and scarlet yarn, and of finely twisted linen—the work of skilled hands. 7It is to have two shoulder pieces attached to two of its corners, so it can be fastened. 8Its skillfully woven waistband is to be like it—of one piece with the ephod and made with gold, and with blue, purple and scarlet yarn, and with finely twisted linen.
Who wore the ephod?
Exodus 28:
Only the ruling high priest wore the complete set of outfits with the golden ephod.4 These are the garments they are to make: a breastpiece, an ephod, a robe, a woven tunic, a turban and a sash. They are to make these sacred garments for your brother Aaron and his sons, so they may serve me as priests.
Samuel wore a plain linen ephod, 1 Samuel 2:
Also, some regular priests, 1 Samuel 22:18 But Samuel was ministering before the LORD—a boy wearing a linen ephod.
On a special occasion, King David wore a plain ephod, 2 Samuel 6:18 The king then ordered Doeg, “You turn and strike down the priests.” So Doeg the Edomite turned and struck them down. That day he killed eighty-five men who wore the linen ephod.
14 Wearing a linen ephod, David was dancing before the LORD with all his might.