Arius, the primary antagonist in Devil May Cry 2, is an insane, wealthy businessman who owns an international company, Uroboros. He wants to find the legendary Arcana, artifacts which would allow him to raise Argosax from the demonic realm and use his power to control the world. Human at the beginning of the game, Arius has access to powerful magic (which enables him to fight demon hunters like Dante) and can create his own demons. Near the end of the game, in Lucia's scenario Arius survives his battle with Dante. Infused with the power of Argosax, he attacks Lucia (first as a demonic version of himself). As he begins to lose, he mutates into a giant creature.
Source: Wikipedia, "[en.wikipedia.org/wiki/Characters_of_Devil_May_Cry%23Arius Characters of Devil May Cry]", available under the CC-BY-SA License.