Dr. Wily

Original Mega Man series
Dr. Wily is the main villain of the Mega Man series. He fought Mega Man himself in the first two Mega Man games, pretended he was good in Mega Man 3 to get a hold of Gamma, got Dr. Cossack to take his place for most of Mega Man 4 by kidnapping his daughter, made Dark Man to frame Proto Man in Mega Man 5, and did a terrible job of pretending to be Mr. X in Mega Man 6. He also escaped from jail and created Bass in Mega Man 7 to ransack Dr. Light's lab for Mega Man's upgrades. He then messed around with an evil energy in Mega Man 8. Not done, he built a gold robot with a giant axe in Mega Man & Bass. He also tried to frame Dr. Light for the robot chaos in Mega Man 9 (and asked for donations to create more robots to stop Dr. Light's, though everyone, including himself, seems to have forgotten that bit), then created a robot illness in Mega Man 10 and begged for donations again to develop a cure, only to use that money on a castle!

Dr. Wily usually attacks Mega Man with 6 to 8 Robot Masters, then with 3 to 5 Fortress bosses, then with clones of the previous Robot Masters, and finally with 1 to 3 giant robots that he or a clone operates. He's very traditional about things.

In Mega Man: The Wily Wars for the Genesis, Dr. Wily finds a time machine, and goes back before the first game to make Mega Man go through the first three games again.

Mega Man Gameboy series
Dr. Wily is also seen in the Game Boy Mega Man games. He's a title character in Mega Man: Dr. Wily's Revenge, in which the plot copies that of Mega Man 2 for the Nintendo Entertainment System, just with the castle in outer space, a theme that would carry on throughout most of the Game Boy games. In Mega Man 2, he steals a time machine and travels about 37,426 years into the future. In Mega Man 3, he uses an oil platform to steal the Earth's water to use for a machine. In Mega Man 4, disrupts a Robo-Expo and uses his previous robots, like all Mega Man Game Boy games, to cause panic and destruction. In Mega Man V, Dr. Wily orders robots named Stardroids to do his bidding.

Dr. Wily created three Mega Man killers Enker for the first Game Boy game, Punk for the third, and Ballade for the fourth. Quint and Terra appear in their place in Mega Man II and Mega Man V respectively.

Mega Man Battle Network series
Dr. Wily is can also be found in the Mega Man Battle Network series, but he's only in the first, third, and fifth games. In the first and third, he is the leader of the WWW (MMBN), which is really, really, evil.

In the first game, Wily isn't too important. He's just "the leader of the WWW." His members are more evil (and weird) than him. But I don't think any other leader would have the style and ambition to design his fortress like a giant skull. I guess he had practice from the original series.

In the third game, Wily is after the TetraCodes, which will unlock four gates that are completely out in the open, yet guard a terrible power: The old prototype of the internet, which is full of pop-ups and viruses and concentrated, gelatinous evil. At the end of the third game, Wily unlocks Alpha thanks to Bass/Forte and unleashes it on the world. Then he gets swallowed by it, disappearing for the rest of the game. Now, normally, this would mean he died. But you know that'd never happen. Not in this series.

In the fifth game, it is revealed that he wasn't evil 30 years ago and had worked with Tadashi Hikari (Dr. Light) to create SoulNet, which links the world's souls together. Forget "double-edged sword," that's probably the easiest way for someone to take over the world, ever. In the ending of the fifth game, he is somehow alive and erases his son's memories to make him be good. What a father.