I don't remember the exact chapter, I want to say somewhere around 70-80, it actually gives the backstory to where he came from. He was actually a slave with no name. He went by a number, i think 22 or 23. There was some type of research lab where the king was doing experiements and there was a homonculous in a jar. It couldn't leave the jar because it would die, and I believe that it was Honenheims blood that helped create/stabilize the homonculous in some previous experiment. The Homonculous in the jar will later become "Father", and is the one that gives Honenhiem his name. "Father" teaches Honenheim how to read/write and about alchemy. One day the king calls upon Father and asks him to teach him about immortality and how to achieve it. Father tells him to dig trenches around the city in a certain pattern and the king has his slaves do so. What the king didn't know was that he was making a gigantic transmutation circle. When it was done, Father told him to stand in a certain spot with Honenheim holding Father in a flask in the center of a circle, and they began. There was a huge flash of light and pretty much everyone died except Father and Honenheim. At this point, the transmutation makes Honenheim and Father(i can't remember if they say Father as well) into living Philosopher stones. Father ends up borrowing Honenheims image and looks just like him. Everyone in the city, including the king, and all of Honenheims slave friends died for the sacrafice to make Father who he is today. So basically, Father tricked the king and everyone else including Honenheim. He spares Honenheims life though for some reason I cannot remember