Gabriel was once one of God's mighty archangels in heaven. He was known as the "Left Hand of God" and served as a messenger of God's word to certain people. He appeared to the prophet Daniel, revealing secrets about his future. He also appeared to Zacharias and to the Virgin Mary, fortelling the births of John the Babtist and Jesus. He was also one of the four archangels whom God sent to deliver his messages to his prophets, including the prophet Muhammad. Gabriel was also the angel sent to destroy Jerusalem.
At some point, Gabriel descended to earth and took on living flesh, becoming human. During his time on earth, Gabriel fought many great battles. At some point near the 1460s he was under the service of the Knights of the Holy Order when he met Count Vladislaus Dracula, with whom he became close friends. However, during a great battle, and for reasons unknown, Gabriel murdered Dracula in 1462. For this crime, God erased Gabriel's memory.
Gabriel spent the next 400 years wondering the earth until one day after a battle, again with no memory, he was found half-dead crawling up the steps of the Vatican.
Gabriel travels to London to investigate a series of horrific, and decidedly supernatural murders, being committed by the mad scientist Dr. Jekyll, in the form of his evil alter-ego, Mr. Hyde. When tracing Hyde to his underground fortress, Van Helsing finds a young woman who claims to be Queen Victoria, and discovers that Dr. Jekyll is in love with the Queen and in order to keep her young has been placed under a spell by Dr. Jekyll that turns her into a young woman for one night. In order to create the potion which causes the transformations Dr. Jekyll needs the drained souls of his freshly killed victims and thus the killings will never stop.
Dr. Jekyll then kidnapps the Queen using the Golden Jubilee Balloon to escape. Van Helsing uses his grappling gun to follow the balloon then proceeds to board it. In the balloon, Dr. Jekyll becomes Mr. Hyde to kill Van Helsing and crashes the Balloon in the process. While fighting on the in-construction London Bridge, Mr. Hyde is shot through the arm but manages to escape.
Upon returning the Queen, Van Helsing says that daybreak will break the spell, returning her to her real age. To reward him, the Queen kisses him, at the precise moment of daybreak, causing her to slap him and call for guards. Van Helsing sends word back to the Vatican about what has happened while he tracks Jekyll to Paris.
The Knights of the Holy Order, stationed at the Vatican, dispatch Gabriel to kill Dracula. He is also tasked with preventing the last of the Valerious family from falling into purgatory; the family swore to kill Dracula nine generations ago and is unable to enter Heaven until they succeed. He is given a torn piece of paper with a latin insignia on it. He is joined by Carl, a friar who provides support and weapons.