Lehah was a member of the Order of St. Dumas before stealing some of thier money and setting himself up as an exotic weapons dealer. His act of betrayal garaunteed retribution by the Order in the form of death by flameing sword at the hands of Azrael. The Azrael that was sent after Lehah was Jean-Paul's father and Lehah was expecting him. Niether party came out of the encounter well, Azrael was mortally wounded and Lehah lost an eye.
Lehah proceeded to murder members of the Order, working west from Switzerland where he attacked the chalet where Jean-Paul was training to be the new Azrael and found his calling as Lord Biis' servant. In one encounter he captured Bruce Wayne, taking him to his oil refinery in Texas. As Azrael Jean-Paul Valley journeyed with Nomoz and Alfred to save him. When Bruce was rescued Lehah was last seen engulfed in the flames of his exploding oil refinery, but he managed to crawl into a pipeline beforethe explosions drove a fragment of metal into his head.
Lehah spent months in a coma before he was stable enough for doctors to operate and remove the fragment. When he recovered he reassumed the guise of Biis and set about exacting revenge on Azrael. Implementing a plan to abduct Azrael he was successful in capturing him but not holding him. Azrael quickly escaped and set about destroying Lehah's security, eventually locking him in a meat locker.
Since then Lehah has made a truce with the Order when they enlisted his aid to stop the rogue Azrael from stopping their release of "The Clench" in Gotham. Biis hasn't reared his head scince then apart from when a group of Dumas followers appeared in Biis' garb when Nomoz tried to re-implant "The System" in Jean-Paul.
As an arms merchant Lehah has access to a huge variety of weapons, assault rifles with teflon tipped bullets or uranium depleted slugs, rocket launchers, cannons and even state of the art defense droids.
Lehah's warped logic can lead him into trouble, but playing mind games with him can backfire.