Lucifer was the first to discover how to harness his powers on Earth, and thus was the one behind the muggings, the initial attack on Maou and Emi, and the mysterious call Emi received at work. This isn't revealed until he and Olba show themselves in front of Maou and co., after he took advantage of Chiho's upset at the scene he had witnessed at Castle Overlord, and held his hostage.
Lucifer succeeded in fatally harming Maou and Ashiya even as they went on the run with Emi. Lucifer destroyed the subway tracks they arrive at. Due to its threatening collapse, enough fear was generated by the crowd of witnesses around them for Maou to return to his demon form, to Lucifer's shock. After being defeated by Maou, he moved into Castle Overlord as well to hide his from the authorities and was given the Japanese name Urushihara Hanzō. Maou purchased a laptop equipped with Wi-Fi for him so that he can help in the research of regaining their powers, using the Internet.