Baruch and Balthamos love each other. They are angels in rebellion from the Kingdom of Heaven. They become part of the Lord Asriel's army of angels and overthrow Metatron, the acting Regent of The Authority.
He is the brother of Enoch, who banished him when he was alive as a human, and who has become the Regent, an angel known as Metatron. With Balthamos, Baruch escapes from the Regent of The Authority in hopes of joining Lord Asriel's army of angels. They seek to bring the bearer of the Subtle Knife, Will Parry, to Asriel and accompany Will without question when Will agrees to go to Asriel only after finding Lyra Belacqua. Baruch's courageous and dedicated nature leads to a fight with the Regent. Fatally wounded and separated from Balthamos and Will, Baruch brings himself to Lord Asriel. After providing Asriel with critically important information, he dies. The last word he utters is "Balthamos", the name of his angelic lover.
His name is possibly a reference to the philosopher Baruch Spinoza, who was estranged on religious grounds from his brother, Gabriel. Baruch also means blessed in Hebrew and is very often the first word used in Jewish prayers.