FMA: The Truth Behind Van Hohenheim - Fullmetal Alchemist, Manga

Fullmetal Alchemist manga differs greatly from the anime. Alphonse remembers the truth, and is able to perform alchemy without transmutation circles. The Fuhrer is Wrath, his son is Pride, Sloth is a giant who is stupid. Greed was imprisoned, and was released in a prison. Kimbley becomes the Fuhrer's top servant, but he's still kind of evil. Anyways, I'll get to the point. Van Hohenheim used to be a slave of the country of Xerxes. The emperor seeked immortality, so he had alchemists use Hohenheim's blood to make a "homunculus", a ball of darkness within a flask. Hohenheim encountered the homunculus while sweeping, and found that he was the "father" of it. The homunculus taught Hohenheim everything he knew, how to read, write, and perform alchemy. He even gave Hohenheim his name. Hohenheim asked what the homunculus would like in return for helping Hohenheim so much, but all he wanted was a body to move around freely. However, the emperor called upon the homunculus, to ask how to gain immortality. The homunculus gave the emperor some orders, and the he filled the out. When everything was set, the time was close. Hohenheim was excited, to see the emperor serve his country as long as possible. Then, something terrible happened. As the emperor gave his blood, everyone began to die. The homunculus did not make a mistake; all who survived was the homunculus and Hohenheim. When Hohenheim came to, he found everyone he knew dead. Then, the homunculus came to be, and was in a form that he wanted to be in so badly, in a form exactly identical to that of Hohenheim. As some of you know, the philosopher's stone is created by human offerings. Many people were sacrificed to make a philosopher's stone, and the one of Xerxes is Hohenheim, and the homunculus, known as "Father", who created the well known homunculus.
Hence, that is why Hohenheim calls himself a monster
Sources:
FMA manga from onemanga.com
Chapter 74 - link
Chapter 75 - link