The International Fleet (IF) grants Ender's parents permission to have a third child, which is ordinarily against the law. The child was Ender. Ender's development is tracked by a monitor until he is five years old. Then he is invited to Battle School. He becomes the youngest child ever promoted into a Battle School army and then the youngest commander ever of a Battle School army. He is a remarkable strategist and becomes the youngest student ever sent to Command School. He is also personally responsible for killing two students who attacked him, but does not know they were killed. Ender ultimately destroys the enemy buggers in battle although he thinks he is only playing a simulated battle game. Ender is a sensitive and caring person, but he can be ruthless in battle or when he feels threatened. After the bugger war, Ender is viewed as a hero, but he doesn't feel he has done anything heroic.
Valentine is the middle of the three Wiggin children. She is just as brilliant as Peter and Ender, but she is kinder than either of them. She protects Ender from Peter's threats while he lives at home. She misses Ender greatly when he goes to Battle School. Peter persuades Valentine to work with him to create new identities "on the nets." As Demosthenes, an online persona, Valentine wields great influence. She also has a strong influence on Ender, which Colonel Graff uses to keep Ender training to defeat the buggers. When the bugger war is over, Valentine uses her influence to make sure Peter can't use Ender as a tool to get more power. She and Ender travel to a far-off colony and later explore other colonies together.
Peter is the eldest Wiggin child. He is brilliant but vicious and was rejected by the International Fleet (IF) because he was too dangerous and unreliable. He resents Ender because Ender seems more likely to be chosen for International Fleet, and he often injures Ender. After Ender is sent away to school, Peter approaches Valentine and asks for her help in launching new identities "on the nets." As Locke, Peter presents himself as a voice of reason and moderation. His influence grows. The treaty that ends the Earth war is named for Locke, and he becomes one of the leaders of the Earth nations. Valentine persuades him to allow Ender to live on a far-off colony, but after Ender writes Speaker of the Dead, Peter asks Ender to write his story as well. Ender does so and publishes it after Peter's death.
As the head of Battle School, Graff watches some of Ender's monitor videos and recruits Ender to the school. He genuinely likes Ender but has little trouble suppressing his affection in order to make sure Ender is the ideal military commander. He accompanies Ender to Command School and tells Ender everything they know about the buggers. After the bugger war is over, Graff is put on trial for what he allowed to happen to Ender and other students. He is acquitted and becomes Minister for the new colonies.
Mazer Rackham is a half-Maori man who was an ordinary soldier in the previous bugger war, 70 to 80 years ago. He ingeniously figured out how to stop the buggers by destroying their queen's ship and was hailed as a hero. After the war, Mazer was asked to leave his family behind and travel at light-speed to Command School in order to be available to train the next military genius. He is a harsh teacher to Ender but an effective one. He supervises Ender through all his battles with the buggers (which Ender believes to be simulations). Mazer is proud of Ender but realistic about life after the bugger wars.