He is the older brother for Nermal.

When Leonard found out that his wife (the Lillith) had slept with and was pregnant by Lucifer, that put Leonard into such a rage, he murdered Lucifer by ramming him with his own horn (the left one). Technically by the bylaws of hell, that made him him the rightful ruler, but he did not want that at all. Especially since history would make it look like he did it for a paragraph and not in a fit of passion.

He panicked, called his young younger brother to help get the body off the horn, and told Nermal that he should be god of Hell instead.



By the way, he and the Lillith tried to make it work, but ultimately are separated now, still married, but separated. He did adopt Leviathan after she was born though



He is designated as the demon of pride. And is the father of the other sins (either biologically or adoptively)