MegaMan.EXE is the co-star of the Mega Man Battle Network series, along with his operator, Lan Hikari. He is this series version of the classic Mega Man. MegaMan's adventures are set in Cyber World, whereas Lan exists in the Real World. He often finds himself saving the world, and usually is usually aided by his friends Roll.EXE, GutsMan.EXE, Glide.EXE and ProtoMan.EXE.
While MegaMan is a program, his soul is human. When Lan Hikari was born he had an identical twin brother, Hub Hikari, who had a heart condition. Hub died as an infant, and Lan's father used an experimental process to digitize his DNA and recreate his body in Cyber World. When he did this, Hub's soul reentered the body of this Navi, and they gave him an outer shell so he'd look and act like any other Navi. Hub is MegaMan.EXE, and Lan wasn't aware of this (MegaMan, however, was) until the end of the first game. Lan's father explains that if he knew MegaMan was his brother, Lan might hold back in battle and err, but now that he understood MegaMan's full potential, he knows telling him won't inhibit him in combat.