"1 And at that time shall Michael stand up, the great prince which standeth for the children of thy people: and there shall be a time of trouble, such as never was since there was a nation even to that same time: and at that time thy people shall be delivered, every one that shall be found written in the book. 2 And many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt. 3 And they that be wise shall shine as the brightness of the firmament; and they that turn many to righteousness as the stars for ever and ever."
- Daniel 12:1-3 (King James Version.)
Michael is the eldest Seraphim, making him the oldest Angel in existence. In addition to commanding the Heavenly Host, he is the head of Heaven's Council. As the highest-ranking Seraphim, he has final say on any decisions or commands, which are then passed to the higher-ranking angels to disperse the orders down the angelic chain. During the War In Heaven in the distant past, Michael personally banished Lucifer from Heaven on God's command.
Michael is a strong but firm leader, maintaining a rigid hierarchy in Heaven. His first priority is the safety of Heaven, and is willing to do, in his eyes, "what must be done" to insure the walls of Heaven are never breached. He follows any order passed down from God without question, as he believes God's will can never be wrong. He sees himself as a good and loyal son to his father, and that is what matters most to him. Due to his borderline zealous trust in his father's commands, Michael doesn't believe in free will, believing instead that everything occurs how God planned it.
As the first Seraphim, Michael is among the oldest and most powerful supernatural beings in existence. When Lucifer began his rebellion against God, Michael was the first he asked to join him. Michael, though he loved his younger brother dearly, refused him, staying loyal to God and his brethren. He lead his forces against those of Lucifer, and ultimately triumphed, though many Angels on both sides died in the conflict. When he cast Lucifer and his supporters from Heaven, he fell into great despair that lasted several decades, blaming himself for Lucifer's betrayal, always believing there was something he could have done to stop it.
Since the beginning of the War between Heaven and Hell, both sides have come to ignore the mortal world, as to focus on mankind's many struggles would give the other side an advantage. That is not to say that they have all turned a blind eye however, as there are rumors that Michael has dispatched agents to Earth, in hopes of giving those suffering under the Fears some degree of reprieve.