Jul had suffered an unhappy childhood. He was initially not accepted into the Sangheilian Academy for Military Education because of his ridiculous name. He changed his name after three unsuccessful years and was finally accepted. He realised that his entire childhood had been wasted and he went home and killed both his parents in a swordfight that destroyed their family home.Years later, just as Jul was about to be conscripted into the Covenant Army, the war ended and the Humans and the Elites made a truce. Disgusted, Jul adopted a loathing of Humans and matters were made worse when news reached Sangheilios that the entire religion of the Covenant was a lie. Most Elites cared little for this, the ones on Sangheilios being the ones who opted to not join the Covenant in the first place. However, Jul was a fanatical believer in the Covenant Doctrine and he refused to abandon his religion. Gathering together a group of other like-minded Elites, the so-called 'Storm' movement attacked one of the sacred Elite temples that was being demolished. They slaughtered all the 'Heretics' who defiled the temple and recovered thousands of documents, databases and artifacts relating to the Forerunners. Amongst them was a special set of Zealot armour, apparently preserved for the 'Didacts Hand'. Jul adopted that title and wore the armour for the next six years. As his faction grew, Jul attacked his next target - a former Covenant Shipyard, now controlled by Humans. He ransacked the place and killed every Human there, and they even managed to steal seven Covenant Warships complete with Slipspace Drives and Weapons systems. They used the information gleaned from the databases they took from the Covenant Temple to plot a course for a Forerunner Shield World - designation 'Requiem'. There, Jul and his minions waited for three years for the planet to become active. They set up camps on the surface and set their ships in orbit around the planet. They destroyed anything that came near to the planet, Human, Sangheili or anything else that dared defile their sacred shield world. After three years of waiting, a battered Human Ship appeared near the Shield World. This was none other than the UNSC Forward Unto Dawn, and on that ship was Johnny Spartan encased in Cryo ever since the Halo event.
Jul initially ordered the Ship destroyed, but after a chance hit by a missile destroyed one of his ships the planet opened and scanned the Human. Jul watched in awe as the planet pulled in three more of his ships, destroying another one in the process. Rallying the remainder of his forces, he ventured into the planet to see what they had been guarding all these years...
When the Storm Covenant enterted the Shield world their first suprise was that there was actually already Covenant living there - Jorgey's Covenant, owned by none other than Jorgey. The Covenant fleet slipped inside the planet's core and took it over, again sparking the Battle of Requiem that had lain dormant whilst the Prometheans slept. Jorgey cared little for this recent turn of events however, and soon departed the planet entirely.
Six months later, however, Jul hadn't made any progress. The Didact, a Forerunner imprisoned within Requiem, was killed by Johnny leaving Jul in charge of the Prometheans on Requiem (at least, those who hadn't defected to Jorgey's side). Jul raced against the Human forces on Requiem to unlock its secrets, eventually coming across a Forerunner artifact that had been held within the planet by the Librarian. Using Doctor Halsey as a means of retrieving the artifact, Jul rejoiced as the two pieces of the Forerunner device were located. However, in a cruel twist of fate, Humans managed to take one of the pieces. After Halsey was shot by the Humans Jul took her away and destroyed Requiem by plunging it into the nearby Star. He escaped along with the remainder of his forces, carefully guarding both Halsey and the Forerunner artifact. He later went on to make friends with Halsey and some people even think that there's something going on there, but the two of them insist that they just have a friendly game of bowling every now and then.
He did, however, attempt to create a clone of the Didact that didn't turn out so well, so after several years of worrying about it he finally decided to go kill it.
After nearly a year of little progress in the field of reclaiming Forerunner technology, Jul had at least established a fearsome fleet of warships and his Promethean forces were expanded when more advanced forms appeared seemingly out of nowhere. Jul was able to muster enough forces to be upgraded from terrorist to warlord in the eyes of the UNSC, and Jul began to invade UNSC colony worlds in search of Forerunner relics. However, Jul's good fortune changed when, during his invasion of the relatively backwater world of Kamchatka, Jul's Prometheans turned on him and began assaulting his forces, and at the same time Catherine Halsey also betrayed him and summoned the UNSC Fireteam Osiris to rescue her from Jul's grasp, and Spartan Locke killed Jul after infiltrating his shrine. Poor Jul eventually died how he lived - trying to run away and swiping his energy sword around uselessly.