An embittered Sangheili, Jul has reason to hate Humanity. You can read his full back story from the Kilo Five trilogy here.
Jul ‘Mdama, the hand of the Didact, seeks to open some sort of Shrine on Requiem. The Capture of Dr. Glassman may aid him in doing so. He believes that if he can free the Librarian from this “Shrine”, she will grant the Covenant Forerunner weappons and technology.