Complex sentence: He worked at Thaxter & Son in Boston, as an apprentice where he became friends with Benjamin Thompson, later knighted Count Rumford to the King of Bavaria, and Henry Knox, a life long friend later a general in the Continental Army.
Split into simpler sentences: He worked at Thaxter & Son in Boston, as an apprentice where he became friends with some other employees who were afterwards well known. Among them were Benjamin Thompson, later knighted Count Rumford to the King of Bavaria, and Henry Knox, a life long friend later a general in the Continental Army.