Mithos Yggdrasill

Mithos Yggdrasill, a half-elf "angel", Hero of the Kharlan War and Leader of Cruxis - or at least, he was. He stopped a war that was killing his own world and draining it of mana by cutting the world in half, creating two that could sustain themselves, which he then ruled for four thousand years as he attempted to find a way to bring his sister back to life. Eventually he was fought and killed by Lloyd Irving and his friends after he refused to accept their goal of uniting the worlds again. The rifts brought him to AM and revived him.

Currently, he is posing as a twelve year old boy who was recently orphaned, and is living with Regina Mills.

Canon History
A half-elf born into a world at war that hated half-elves, Mithos and his sister Martel did not have an easy life from the start. They were forced out of the elven village, Heimdall, after being blamed for an unrelated incident and wandered the world, often going without food or falling sick due to the cruelty they were shown by humans. When they heard that Sylvarant was invading Tethe'alla, they went to the capital to warn the opposing nation, but were ignored due to their race. The capital fell, but they gained a travelling companion in Kratos Aurion, and later in another half-elf, Yuan Ka-Fai. As Kratos taught Mithos swordsmanship, he vowed to change the world and stop the war - which, due to the increasing drain of mana as an effect of magitechnology weapons, was killing the Great Tree which gave the world its mana. To this end, he singlehandedly made pacts with every Summon Spirit - elemental beings which controlled mana - and then had Kratos make a pact with Origin, the King of Summon Spirits. Origin made for him the Eternal Sword, a blade that could cut through and control time and space.

While trying to stop the war, they came upon a human who was severely injured. Martel healed him, only for the soldier to then kill her. Kratos and Yuan killed him in turn, and Mithos, distraught, held her soul in stasis inside of her Exsphere. Then, he used the Eternal Sword to cut the world into two parallel ones, which vied for the remaining amount of mana in a neverending cycle, effectively stopping the problem of magitechnology and halting the issue of another global war. He then stored Martel's soul inside the Great Seed - the remnant of the Tree after its death - and took it to the elves' ancestral home of Derris Kharlan to protect her until he could bring her back to life.

Mithos then began his reign over both worlds, establishing the Church of Martel and the Journey of Regeneration, which reversed the cycle of mana depletion in the two worlds. He manipulated history so that he became a hero and Martel a goddess. Over four thousand years, he bred the Chosen of Regeneration and turned them into angels, seeking out the one who would make the perfect vessel for his sister. His actions eventually caused rebellion - Yuan created an opposing force to disrupt his plans, and Kratos fled and took a human wife, though he returned to serve Mithos after her death. Mithos established both a religious authority and a terrorist group who put pressure on the world - known as the Desians - and also oppressed humans, forcing them into human ranches and using them for the production of Exspheres.

Due to Martel's dying wish for a world without discrimination, Mithos used an advanced form of Exspheres - known as Cruxis Crystals - to mutate half-elves into angels. This process made them almost immortal, without a need to eat or sleep. It was his wish to turn everyone into "lifeless beings", as then there would be no hatred of others or discrimination for those who were different.

His twisted ideals eventually brought his downfall, as Kratos' son, Lloyd Irving, and his friends discovered the truth behind the Journey of Regeneration and the purpose of the Chosens, and then fought against him. Mithos grew to admire and like the group, as he spent some time infiltrating it in his true form, growing especially close to another half-elf, Genis Sage. Strikingly, he and Lloyd were incredibly similar, but while Mithos was alone and incapable of reflecting upon his mistakes and changing, Lloyd could admit that he was wrong.

It was this difference that broke Mithos when he revived his sister and she rebuked his actions. Unable to cope with the reality of the situation, he fled to Derris Kharlan, forsaking both worlds to die. It was also this trait that allowed Lloyd to fight him and win, though he didn't like being forced to kill him. Mithos died without regrets, acknowledging Lloyd as his shadow who had walked a different path.

AM Canon
Of course, this was all then ruined by Mithos awakening, not dead and without any sense of purpose. Unable to figure out why he was alive once more, and in an unfamiliar place, he found Regina Mills and passed himself off as an orphaned child, intending to use her to acquire information about this new world and the rift that had somehow brought him here. Since then, he moved to Storybrooke and started to live with her.

Being an angel, he took advantage of his mobility and made several excursions to other areas - encountering Nyarlathotep, Yu Narukami and Alexander Anderson.

A spell cast by Regina and Mr. Gold trapped him, as well as quite a few others, in the Enchanted Forest - a situation that could mean revealing some of his power in order to get back.