Psalms 105:36

He smote also all the firstborn in their land
Both of men and beasts; the firstborn of the king on the throne, and of the maidservant behind the mill, and of the captive in the dungeon; this was the last plague, and which prevailed upon the Egyptians to let Israel go, ( Exodus 11:5 ) ( 12:29-33 ) .

The chief of all their strength;
or the first of their strength; the same in different words as before, their firstborn; see ( Genesis 49:3 ) .