Andrew "eNDER" WIGGIN
Ender was one the most brilliant and youngest qualifiers for Battle School. At the age of five, he accepted the offer to leave his family and join the school. He's careful to keep to himself and avoid unnecessary interaction with others, yet he's always a step ahead. Not too long after he established several hostile relationships with other students, we was given his own official "army", the Dragon Army, to compete with the other, older kids' armies. Though the Dragon Army was disbanded due to it's amount of loses, Ender inverted the reputation and he became commander of a nearly invincible army constructed of all younger students. He would later become the youngest in history to graduate Battle School and advance to Command School.
PETRA ARKANIAN
Petra was an aggressive female student who attended Battle School. Originally part of the Salamander Army, she eventually became commander of the Phoenix Army after proving herself. Though, early in Ender's Battle School life, she helped him develop more efficient combat techniques, thus somewhat helping him obtain his reputation. However, Petra was careful not to tell her colleagues of such aid, as they look down upon her enough for her gender.
BONZO MADRID
Bonzo was a violent boy and the Salamander Army's commander for a time. After Ender was promoted to the older kids' armies, Bonzo served as his commander. No one (up until Ender) went against his orders. He made sure his team understood obedience, but Ender saw flaws in his battle plans and sacrificed "obedience" to save the Salamander Army from a loss on more than one occasion. Bonzo gradually lost respect from his army and, after a physical fight with Ender, ultimately left Battle School.
aLAI
Alai was the closest thing Ender had to a friend at the Battle School. He helped Ender with additional training, much like Petra did. He was one of the few students who was never hostile to Ender, or rather, jealous of Ender. Later, he proved himself capable enough to graduate Battle School and advance to Command School, though years after Ender did.
dink meeker
In the Rat Army, Dink was Ender's platoon leader after Ender was transferred there from the Salamander Army. He never trusted the teachers and staff of Battle School and always considered them as his enemies. Nonetheless, we would also advance to Command School and meet Ender again, along with Alai and Petra.
bean
Bean was a part of Ender's Dragon Army in the Battle School, but he occasionally disapproved of Ender's methods. He was similarly as brilliant as Ender, despite his age and small size, it took a while for respect to develop between the two. He would later meet Ender in Command School and help in the protection of Earth.