Genesis 37:36
And the Midianites sold him into Egypt unto Potiphar, an officer of Pharaoh's, and captain of the guard. officer: Heb. eunuch: but the word doth signify not only eunuchs, but also chamberlains, courtiers, and officers captain...: or, chief marshal: Heb. chief of the slaughter men, or executioners

Genesis 39:1
And Joseph was brought down to Egypt; and Potiphar, an officer of Pharaoh, captain of the guard, an Egyptian, bought him of the hands of the Ishmeelites, which had brought him down thither.