MegaMan.EXE is one of the two main characters in the MegaMan series 'Mega Man Battle Network'. He is a computer program (called a Navi) which is used by Lan Hikari (the other main character) to go onto the internet.
He is very friendly with Roll.EXE, the Navi used by Lan's friend, Mayl. ProtoMan.EXE, owned by Load Chaud, is his main rival.
As you beat enemies in the game, you get chips which MegaMan.EXE can use to perform special attacks, like the powers in the MegaMan and MegaMan X games. There is a lot more of them, however. And I do mean a LOT. There are 175 in MMBN 1 alone. Sometimes by selecting several chips at the same time, MegaMan.EXE can combine them into a more powerful chip. This is known as 'advancing' the chips. An example is selecting Cannon A, Cannon B and Cannon C. The chips will 'advance' and become Z-Canon 1.
You can buy and find powerups for MegaMan.EXE. At first he starts off only able to cause 1 damage with the Mega Buster, but by the end of the game he can cause 6. This may not seem like a lot. However, factor in the fact that a fully charged buster does 16x the normal damage... 96 is a lot more damage than 16. He can also upgrade his Charging speed and the rate at which he can fire the Buster. You can get Armour for him also, in three different elemental kinds, but disappointingly it does not change his sprite. (However, it apparently does in MMBN 2. It's not out outside of Japan yet though and as I want to buy it I'm not going to get a Rom to check this)
*WARNING* *MASSIVE SPOILER AHEAD ALERT* *WARNING*
*DO NOT READ IF YOU HAVEN'T BEATEN BATTLE NETWORK 1*
MegaMan.EXE is actually a computer program of his twin brother, Hub, who died. His father was trying to make a Navi with true AI, but couldn't. He then tried basing one on Human DNA, however 5% of it couldn't be coded. When Hub died, he used Hub's DNA to make a Navi for Lan. However, he had to alter .001% of the DNA or else MegaMan.EXE and Lan would 'synch' and everything which affected one would affect the other (I don't get how this would work either. But it's only a game, so who cares?). Near the end of MMBN 1, however, they must fix the DNA so that MegaMan.EXE can survive an attack, so apparently they are 'synched' now. Have to wait for MMBN 2 to see if this is true or not.