Michael

"There's a part of me that wishes I didn't have to do that, but you gave me no choice when you broke the rules"

-Michael to Nathaniel

History
Arguably one of God's first creations was Michael, the first Archangel, the first of the four archangels: Lucifer, Raphael and Gabriel, and the very first angel in general. Before life, the Earth, and even the universe itself existed, Michael and the other archangels fought a war with God against the Darkness, whom God tricked and sealed away using the Mark.

Upon imprisoning the Darkness, Michael looked after Lucifer and personally raised him, taking care of him in, as he said, "a way that most people could never understand". He also mentioned that while living in Heaven with God and their siblings, Michael and Lucifer were happy together.

After God locked away the Leviathans in the monster realm Purgatory and after he started the creation of Heaven and its angels and Earth and its people, he commanded all of the celestial beings to bow before mankind, asking them to love humans more than him. Though Michael obediently did so, Lucifer questioned this order, insisting that they are "broken, flawed abortions." Lucifer then sought out Michael for support, but Michael refused to listen and therefore, under God's orders, cast Lucifer out of Heaven. When Lucifer had corrupted man and created demons, Michael, again under God's orders, cast Lucifer into his cage. At some point, God left Heaven and Michael assumed command of the angels, running Heaven and Earth (and possibly the entire universe) for millennia.

When demons began making plans to free Lucifer, Michael decided to allow the seals binding Lucifer to be broken. He and a group of other angels, including Raphael and Ezekiel, wanted the Apocalypse to occur so that he and Lucifer could battle. Michael expected to be victorious, so as to bring about paradise on Earth. Lesser angels, like Kemuel or Emmanuel, were not privy to the plan and were deployed to make it look as though Heaven was fighting the Devil's release. However, those angels that did learn of their plans (like Nathaniel) were either forced to cooperate with their plans or were cast out of Heaven.