This manga is actually sad, with all of those powerful robots that died including Gesicht. Fortunately, Atom survived with the help of Gesicht's memory chip and the one who did the job is a human scientist and also Atom's father or creator, Dr. Tenma. 

Talk about Pluto, I don't know if I should get mad at Sahaad because in the story, he was just a victim fueled by anger due to what happened to his father Goji who calls himself Dr. Abra. Goji used his anger to manipulate Sahaad (aka Pluto) into committing those crimes of which Gesicht was specially assigned. To avoid the conflict here, Goji lost his life in the war but what he believes in is that he is a cyborg (robot with human parts) and what he didn't know is that he is now a robot created by Dr. Tenma as well. This part really shocked me. I'll stop here, it's coming to the ending part if I keep telling.